@Powerslaty when you installed the package it should've given you instructions on how the game is launched.
You need to place the game files in ~/.local/share/soniccd/, which should be a Data.rsdk file and some movie files in a subfolder called Videos.
You can get those files from either the Steam release of Sonic CD or the mobile releases (Android for exampleo is free to play with ads so you can get the APK for free).
The Sonic Origins Data.rsdk won't work due to changed scripts and I believe only the videos from the Steam release work, because the fan engine doesn't handle the format used in the mobile ports.
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luluco250 commented on 2021-10-20 17:44 (UTC) (edited on 2021-10-20 17:44 (UTC) by luluco250)
Upstream seems to have fixed Linux builds, the resulting binary has been renamed to "RSDKv3" so I adjusted the PKGBUILD and launcher accordingly (it'll use the new name for the binary but the launcher remains the same).
The install script will notify about the change if you upgrade from a revision older than 377.