I use syncthing to sync almost everything across my computer, laptop (occasional usage), server (RAID1), old laptop (powered up once every month or so), and a few other devices (that only get a small subset of my data, though). On the computer, laptop, and server, I have btrfs snapshots (snapper). Overall, this works very well, I always have 4+ copies of my data in 2+ geographical locations.

Probably its part of Flatpak?

I took my existing JPEG file, compressed it using JXL, 15% smaller.

Then I decompressed it again into JPEG. The file was bit-for-bit identical to the original file (same hash). Blew my mind!

Directly using JXL is even better of course.