The problem is nothing to do with btrfs itself, synology intentionally disabled its usage on specific models in a firmware update (supposedly because it wasn't supposed to be enabled in the first place - but had let or allowed people to do so for some time).

And there was never a problem with ZFS apart from the kernel team intentionally re-licensing symbols to block ZFS once they saw the ZFS team using them ;)

Yes, but they disable btrfs in firmware upgrade, without providing any ways to migrate the data.... This is not good customer experience, don't you agree?