Project sync is best achieved with the online version, but if you prefer to use the standalone, I guess Syncthing is a great option too! If you are looking for the correct folders to synchronize, you will find answers here: https://microstudio.dev/community/help/standalone-version---where-are-project-fi...
The 50 mb limitation is only for the online service, the standalone does not have such limitations.
Note that you can also get more storage on the online service by subscribing to my Patreon: https://www.patreon.com/microstudiodev :-)