There are a lot of ways to lose that though. No rsync able to run and calculate block checksums on the other machine -> no block syncing. Change a byte in a file in an encrypted volume -> it might copy-on-write and make a wholly new encrypted "file" with everything different in the final encrypted data. Etc, it depends on a bunch of stuff interacting in ways that they might have legitimate reasons to not support, particularly with security/privacy sensitive stuff.
Not sure what you're encountering, but if it's important to you there are a few ways to troubleshoot it. It might be possible to get it working.
Dropbox syncs the deltas in LUKS and veracrypt disks. A change of a bit in plaintext changes the blocks that are involved, and only those blocks are updated. But most other sync tools don’t handle it properly.
That was around a decade ago. Today, one would use cryptomator, rclone, gocryptfs rtc.