I was trying to install Amazon Games on my Lutris installation on my old laptop and ran into a curious situation. I was able to complete the installation ok as I was able to log into the Amazon Games launcher and install a game. However, I noticed that there was a command line terminal window from the installation process still running in the background even though the installation had proceeded successfully. According to this window, the installation was not complete and the only option I had was to Abort.
I was trying to install Epic Games on my Lutris installation on my old laptop and ran into the following error message:
Exit with return code 256
(This appears to be a common issue and is not necessarily limited to Epic Games.)
I actually removed my default Ubuntu package which was a few minor versions behind the official packages. I then installed the latest version of Lutris directly using a .deb file from their website.