My use case was probably simpler than some peoples use of syncthing as I just use it for backing up photos/messages/settings and dont need it to be instant.
My only issue with FolderSync is that its proprietary but its the only option i found that worked well. The various rclone frontends that exist also didnt work nicely with the webdav server I use so I settled on it, its very polished so I dont mind too much.
10 euros for an Android license for or $28 (yes they use two currencies on one page) for a desktop license. The free ad supported version on the play store has over a million downloads.