@Mushoz I was able to complete the installation by going to Steam > Settings > Downloads > Clear Download Cache while the download was running. This causes steam to restart, bypassing the window with the "Cancel" button; the installation then continues normally. However, this issue still prevents one from being able to launch the game. (I am referring to AC:II 33230, haven't tried with Brotherhood)
You need to have the game activated through windows or wine. To bypass the key not loading you need to edit ~/.steam/steam/appcache/appinfo.vdf . Edit the line with the text "legacykeyregistrylocation^@HKEY_CURRENT_USER\Software\Valve\TestApp48195\SteamKey" edit it to "legacykeyregistrylocation2^@HKEY_CURRENT_USER\Software\Valve\TestApp48195\SteamKey". With this typo steam will start the game without loading the game key.
The uplay version bundled with brotherhood is to old to run so you need to manually install the latest version with "WINEPREFIX=/home/{USERNAME}/.steam/steam/steamapps/compatdata/48190/pfx wine Downloads/UplayInstaller.exe" After this the game will run fine.
The workaround from @tijder does not work anymore as the steam client will check the integrity of appinfo.vdf when launching.
The cause of this is the same as #190. See https://github.com/ValveSoftware/Proton/issues/190#issuecomment-727183666, https://github.com/ValveSoftware/steam-for-linux/issues/5649#issuecomment-727183485 and https://github.com/ValveSoftware/steam-for-linux/issues/212#issuecomment-727181364 for the same issue and the current status.
I am trying out different games from my Steam library. Installing Assassin's Creed 1 works fine and plays correctly. However, when I try to install Assassin's Creed Brotherhood or Assassin's Creed: II a Window that says "Creating Local Game Files" pops up. This screen never completes.
In the background I do see the game being downloaded with progress going from 0% to 100%, however, said screen remains. I can only click "cancel" or the cross in the rightmost corner of the popup, but both will uninstall the game immediately.
FYI, Assassin's Creed Brotherhood runs fine when I run the Window's version of Steam through regular Wine. One thing I noticed is that this version uses Ubisoft Uplay Launcher to launch the game. Perhaps this is resulting in installation conflicts with Steam Play.