On the positive side..

With unannounced changes to the Adobe Cloud/Desktop processes done probably in an Feb 14/15 update (which I until now could get only by killing Adobe processes and downloading/installing a new fresh Desktop install), suddenly my "Desktop" has begun starting on its own on reboots.

The Desktop itself has not changed version, but its underlings have.

Sinde Oct 2019 (introduction of the ugly version 5.x desktop) it has not managed to start on reboots a single time until after the versions shown for 2/14.

Desktop and Apps stayed on version 5.0.0.354 the whole time, but Core Sync and CC library were changed.

So maybe the Desktop is working better now. It has managed to start by itself three times now.
(Still ugly as sin, tho. :-) )

See attached version setup from 2/8-2020 and 2/14/2020.

@Bruce,

I have unfortunately experienced that random "self-fix" many times. Suddenly it manages to start up without problem. (Simply means that it manages to start a session (or finds the right existing one to match to).

I have seen it magically pop up, after clicking "Help -> Updates" in Photoshop. (Since that menu these days merely call up the Desktop.)
Or once, I opened an Illustrator doc, where the used Adobe fonts were claimed as disabled. Illustrator then goes through the font replacement dialog, and when clicking in to enable the fonts suddenly POP GOES THE WEASEL, and the Desktop randomly springs up in front of me to occupy most of my screen, looking at the Font list. Then the Desktop overall suddenly ran fine (until next reboot).

Those rare successes always goes away again whenever I reboot.. After it manages to start once, it keeps running well, UNTIL the next reboot.

Last time I tried a stranger case was yesterday.
Desktop would not start at all.. On a hunch, I went to my Adobe Account on the web under Active Sessions and closed all sessions. Which should then disable all the apps AND the Desktop, until I log in again.

Starting the Desktop immediately after it sprang up like a flash, shoved me through an Adobe login process, after which it started running just fine. It also created a fancy new session in the Adobe account on the web. All was well it seemed.
I thought Heureka, I found it; the Desktop app just cannot figure out how to match itself to sessions.

Desktop ran fine, to test I then Quit and restarted it several times. All fine.

Then my final test.. Rebooted my system after killing all sessions in my account again.
No automatic startup of the Desktop happened. Tried to start it manually, I was RIGHT BACK to the long wait with spinning wheel for the final letdown "Quit or Repair" dialog.

I have not been able to start the Desktop since, despite many tries.

Most unstable, least robust software EVER, but likely this startup issue is merely a small bug mishandling the session creation/login process. With a simple fix once someone actually look at debugging it.
Everyone so far just points to all the Repair, Remove, Adobe Clean Tool, reinstall Desktop, remove all apps, reinstall apps, support pages. None of which will ever work, since this is a BUG in the desktop startup. As the logs clearly show.

The Adobe Account also shows, that when the desktop fails to start, no session is created in your Adobe account. EVER.. That is where it fails. Between "Adobe Desktop Service" and "Adobe CEF Helper", who are apparently responsible for creating a valid session to Adobe, they fail to do so, and "Creative Cloud" kills them and shows the "Quit or Repair" dialog.

The lack of new session creation is more easily seen if you first click "End All Sessions" in your Active Sessions list in your Adobe web-account. To clean it out. There will then be only one (the current web-login your browser is running), and when any of your local apps (including the Desktop app) start up, their first responsibility would be to create a new session by making you login.

That works fine if you test by just starting Photoshop, Illustrator, or other app. They will proceed to log you in.
With the Desktop app, I only managed to see it do that this one time. Manage to log me in, and a new session is listed on the web.

At the risk of jinxing myself, my CCD may have healed itself. I quit trying the fixes Adobe recommends about 10-days ago. Yesterday and today, CCD started first time; not because I did anything to correct the problem. Keeping my fingers crossed.

The repairs are not actually necessary. I have tried that OVER and OVER. Same with all the various support pages (and support people) claiming to "repair", download a new copy, Use Adobe Cleaner tool, uninstall all apps, rename OOBE folders, ..., ..., ...

The final "Quit" or "Repair" message is simply the dumb desktop's final claim when it "gives up" on starting the Adobe Desktop Service. Which apparently is failing to create a session with Adobe.
A bad assumption of "well, if my services are not working, then it MUST be because the installation or the system is bad. Certainly can't be buggy Adobe Software. So Mr/Mrs user, could you please reinstall or buy a new fresh system to install on".
NOT very robust software. Not able to handle or report errors intelligently.

The issue is a BUG in the new desktop where it cannot figure out how to create a valid session to get started.

In all my failed startups, the ACC.log consistently show the same failure scenario.

The short story:

- GetUserProfileXml: No access token present. User not signed in.

ADCS goes into
- executeStateMachine(): state loop: Workflow: INIT, State: WAIT_FOR_SIGNIN

then waits with a 30 second timeout set.

- executeStateMachine(): waiting for SignInComplete

ACCC POSTs an ACCC_BROWSER_STATUS event of ACCC_BROWSER_LOAD_ERROR.

Then 30 seconds later the timeout expire, and CCD reports

- LoadTimeLogs: ADS seems to be hanged. No response upon pinging.. ADS/Vulcan issue...Killing ADS & Vulcan
- LoadTimeLogs : PingMissCount crosses pingMissThreshold. Launching ADS Service Executable
- PingMiss more than threshold. Looks like ADS is crashing continuously
- No point in launching ADS again. Showing corruption dialog

The "Corruption Dialog" mentioned right above in the log file refers the final "Repair" dialog.

I would assume that at some point in that scenario maybe there should have been a popup or screen with a Login, but no such thing ever happens. It fails to find credentials and fails to ask for any login.
So, ADS (Adobe Desktop Service) simply hangs around until its master (Creative Cloud) realizes that there is still no login completion, and then kills both ADS and the IPCBroker process. The Adobe Crash Reporter then runs, and presumably reports a crash to Adobe. I must have thousands of these reports up there by now. Apparently no one is following all these Desktop failures.

While these retries are going on, the Creative Cloud app is looping incessantly (eating away a full core/thread by itself), and the "Adobe CEF Helper" (I assume fronting the Chromium libcef.dll library) is spinning up in bursts repeatedly, then going to sleep again.

I had this numerous times and culminating in PS & LR coming to standstill. had a week long nightmare with Adobe and Apple to resolve it, I was bewildered when I asked on numerous occasions that if this error notification ( To quit or repair cc ) was made then surely Adobe know the issue, it got nowhere. lots of things were 'Tried' and ended up with me not being able to open either to 'check the path to back up ' so I could reinstall OS and CC apps , ,, ya never guess what when I had given up and resigned myself to maybe not being able to restore my back up of my catalogue?.. it done it self and restored my cat when I completely deleted PS /Lr and reinstalled. .. I remain an ardent user of PS/LR as I am a photographer, but... support has gone way down on my expectations and I'm considering seeking compensation for their oversight that cost me the loss of a deadline for work and nearly ruined me.

None of the repairs suggested by Adobe worked. I could not delete all the files from the OOBE folder as Adobe suggested because Windows 10 said the three database files were currently being used by Adobe. This was not the case since I attempted to delete the files immediately after starting my computer and before even touching the CC Desktop application icon. I am starting to get hopeful thought. CC Desktop opened on the second try this morning. Hope I am not fooling myself.

I don't know why no one from Adobe is responding to this. It keeps happening to me and I am getting upset!

yes, same as me, while open the application, always ask me to repair. So disturbed.

I think there is something significantly wrong with the new CC Desktop. It use to work about 40% of the time. The last two days it is averaging 0%. I have to open Lr directly. I am using Windows 10. The previous version of CC Desktop worked great every time.

Hi.
I also get the message and when I repair it, it gets stuck at 42 % and uninstalls my existing Adobe desktop.
Also need help on how to fix it.

Same thing here, going on the 3rd time tonight.