Maybe my use cases are too simple, but why did you find SyncThing a bad software? In my experience, understanding the setup was the difficult part, but that's to be expected when you're used to cloud providers managing that on their end. Apart from that, it doesn't work on iPhone or iPad, the syncs can take a couple of minutes, and that's all the cons I can think of.

The big pro for me is being able to sync files that an overzealous cloud provider might autosanitize without asking.

Regarding Google Drive on Linux, I've tried InSync and it worked so well with a combination of Dropbox+Google Drive+Google Workspaces that I bought the lifetime license. From time to time they do 50% offs, so it's even more attractive. Much better experience than the official Dropbox client.