Alright, let's first make sure you fulfilled the minimal Requirements:
Inside the Folder where you cloned the Repo to try:
inside you should have these 2 Folders as Symlinks:
- RSDKv5 -> which points to the Root Directory of the RSDKv5 Repository
- Game -> which points to the Root Directory of the Sonic Mania repository
to verify this worked try:
Bash:
ls -lsa android/app/jni/RSDKv5/
Bash:
readlink -f android/app/jni/RSDKv5/
and
Bash:
ls -lsa android/app/jni/Game/
Bash:
readlink -f android/app/jni/Game/
Both should return a list of Files and Directories and the Destination of the Symlinks you created.
Next make sure that you've installed the Dependencies:
Then make sure that you've compiled the Shaders according to this Readme File:
https://github.com/Rubberduckycooly/RSDKv5-Decompilation/blob/master/RSDKv5/Shaders/README.md
The Developers of Sonic Mania actually recommend that you use Android Studio to build the Project. Install Android Studio and open the Folder android/ in the Root Directory of your Repo as a Project. Android Studio should now ask you to install NDK and probably a few other Packages. Just do whatever Android Studio asks for and then use the Menu to trigger the Build Process.
Good luck!