To access your legitimate copy of the data.rsdk file, you must first own the game on a PC platform.
A popular tool where you simply drag and drop the data.rsdk file onto the extractor to generate "data" and "unknown" folders containing sprites and media. sonic mania plus data.rsdk
Because the game assets are encrypted within this archive, you cannot simply open it like a ZIP folder. Modders use specific tools to "unpack" the contents: To access your legitimate copy of the data
Navigate to your install location through the Manage menu next to the "Uninstall" button. sonic mania plus data.rsdk