It seems you’re asking about the data.rsdk file from Sonic Mania Plus . This file is the main game archive that contains assets like levels, sprites, sounds, scripts, and more.
Sonic Mania Plus uses the audio engine. Inside data.rsdk , you will find .ogg music files (the PC version) and sound effect banks. The Plus content adds new jingles for Mighty and Ray. sonic mania plus data.rsdk