Encryption was working fine with for me on f2fs.
IIRC we have a metadata partition so the -16kB length shouldn't be a problem.
Here you have an unsecure boot to get logs while encrypting/decrypting (probably 13.0 but could be 14.1).
Maguro take long time to encrypt (around 20 min) right after a wipe.
On z3 thread we have lot of troubles with magisk and co breaking some part of init scripts who can be the source of your troubles.
I just encrypted my hitherto-unencrypted second GN running L 13 from August 12th. It went fine and I could reboot without problems.