The Microsoft Store version frequently checks against the Xbox Cloud. If the local save doesn't match the cloud, the game may prompt you to choose one. Choosing the wrong one could overwrite your progress or the new save.
While using a save game can save you hundreds of hours, it is not without risks: forza horizon 5 100 save game microsoft store link
Search for creators who provide "MediaFire" or "Google Drive" links in their descriptions, but always check the comments for feedback on whether the file currently works with the latest game update. The Microsoft Store version frequently checks against the