Watch Dogs 1 uses a version of UPlay so old it fails in a different way. I get this error..

After using the method described above the game installs Ubisoft Connect correctly and at this point updates my now old installer that I downloaded to the latest version, detects my previous sign in and launches the game without issue.

Overall these third party DRM launchers like Ubisoft Connect and EA Origin should have automatically updating dependencies that install upon fist launch instead of shipping with a certain version then relying on legacy support in order to get the DRM launcher up to date.

I think some of the games (I've got only one of them so far, a reboot of Flashback) using Ubisoft launchers just got updated recently to use a new depot, an Ubisoft Connect one. While this eliminated the issue w/ updating/replacing launchers, the "Looking for patch" loop issue is still here for both 6.3-8 and current Experimental. I'm in fact recalling some upstream patch included in 6.22 addressing that issue (and it's definitely included in current Proton-GE, which behaves normally for Ubisoft Connect for that game).

Patch notes for aforementioned game update: https://steamcommunity.com/games/245730/announcements/detail/3148575800209543740

Also, I was wrong about the Wine upstream fixes for Ubisoft Connect, I've seen it on Proton-GE-6.21 release notes, stating this:

-Fsync has been disabled on all Uplay titles -- it causes Uplay to hang on "Looking for patches" when initiationg a new prefix. Esync works fine.

I'll probably retest Flashback (245730) with FSync disabled.

Ok, can confirm that running the game with PROTON_NO_FSYNC=1 %command% eliminated the "Looking for patches" issue with 6.3-8.

Currently neither of the alternatives work anymore, at least for me. UPlayInstaller.exe dependency was already updated to UbisoftConnectInstaller.exe as requested by @ChaosBlades, but it is getting stuck into the "Looking for patches" anyway:

And running the game with PROTON_NO_FSYNC=1 %command% as suggested by @thaewrapt doesn't make any difference.

This is an issue for me as well. I tried all versions of Steam Proton. None of them worked. Any workaround?

To get past the "Looking for patches" error I had to disable both Fsync and Esync. After the update I re-enabled them.

Apparently, Proton's latest version fixed the "Looking for patches" issue. I simply installed steam on my Ubuntu, enabled Proton experimental in the config and launched the same game that was giving me the problem back then (Assassins Creed Chronicles: India) and everything worked smoothly out of the box. No need of PROTON_NO_FSYNC=1 %command% or disabling Fsync and Esync.

Have tried a while to get Assassin's Creed Origins working until I finally found the instructions of the OP, which was a quick workaround to get the game finally running on Linux. (UPlay just didn't work)

I also checked how it would behave on Windows, and it certainly used UbisoftConnect and the UbisoftConnectInstaller.exe is present in the game's root folder. Not sure if it used UPlay as an intermediate step, I could recheck.