Sonic Forces: Speed Battle is a server-side competitive game, making private servers complex to implement and often leading to bans due to the game's always-online nature. Community efforts to create private servers or use modded clients typically aim to bypass progression walls, access characters like Shadow and Super Sonic, or address pay-to-win mechanics. You can find a review of the official game at MiniReview. Sensor Tower

Party Matches: This is the official way to play privately. Using a Party Ticket, you can host a room and share a code for friends to join, ensuring you only race people you know rather than random opponents.

Setting Up a Sonic Forces Speed Battle Private Server

Server-Side Storage: All official game progress is stored on SEGA's servers. To ensure your data is safe, link your game to a Google Play Games or Game Center account in the settings menu.

I have lost my progress, how can I recover it? - SEGA Support