Flatpak

You will need the FreeDesktop.org 21.08 SDK installed, if you don't have it, install Flathub which provides it.

Sonic CD (Original Steam Version) Flatpak

First, go to your Steam library, right click on Sonic CD and click Manage > Browse local files. Copy the Data.rsdk file and the videos folder into this directory.

To build and install the flatpak, run:

System-wide:

$ sudo flatpak-builder --install --force-clean soniccd com.sega.SonicCDSteam.json

User:

$ flatpak-builder --user --install --force-clean soniccd com.sega.SonicCDSteam.json

Sonic CD (Android Version) Flatpak

This method will not install the video files, as the decompilation only supports video files from the Steam version.

First, you need to install the game on an Android device. To get it, visit https://www.sega.com/games/sonic-cd.

Once you have the game, use a file manager on your device to navigate to the directory Android/obb/com.sega.soniccd.classic and copy the patch.[number].com.sega.soniccd.classic.obb file into this directory as Data.rsdk.

To build and install the flatpak, run:

System-wide:

$ sudo flatpak-builder --install --force-clean soniccd com.sega.SonicCDAndroid.json

User:

$ flatpak-builder --user --install --force-clean soniccd com.sega.SonicCDAndroid.json