Supports a ton of back ends, self hosted, and commercial options. You can transparently encrypt with private keys you control.
I personally use B2 Backblaze for storage.
My phone backs up every night and Round Sync pushes them to B2. On my desktop I can mount as a volume. I can also access my storage from my phone going the other direction.
I’ve done the same using SFTP if I don’t want the overhead of persistent file storage.
It does not support indexing or previews for searching or finding say a photo. You can put whatever you want for data. So I have caches, indexes, and thumbnails that work in Linux. I can’t really make use of those on my phone though.
Rclones bisync feature is also a bit dangerous when I tried to use it a year ago. I more than once “deleted” everything. B2 doesn’t delete by default, just hides, so I was able to recover. I now do unidirectional syncs from my machines to different buckets until I’m motivated to investigate a proper 3-way merge solution.