I had the same "unable to detect uplay" error except for a different Anno game. Here's how I solved it, if you want to try:
- Install ProtonUp-Qt, then add SteamTinkerLaunch using it.
- In Steam, go to Properties... for the game that needs Ubisoft Connect. Then Compatibility tab, check "Force the use of a specific Steam Play compatibility tool", and select "Steam Tinker Launch" from the dropdown.
- Start the game, and quickly press the "MAIN MENU" button at the bottom of the window.
- Click "One time run", choose the UbisoftConnectInstaller.exe that you downloaded and click "RUN COMMAND"