Your save file is cryptographically tied to your account's unique identifier (XUID). Advanced save swapping requires converting the downloaded save to your XUID using tools like Doliman's Crypto Tool and 010 Editor with custom templates. This is an advanced process and not recommended for beginners.
To reduce ban risk, many players load the save file while steam/Xbox is set to offline mode to test cars locally. forza horizon 5 pc 100 save game upd