After the move to a post 5.0 kernel Adiantum has become available.
Adiantum is an encryption mode created by Google specifically for devices without AES hardware acceleration, like all the Raspberry Pi models, and can provide significantly faster encryption and decryption speed for both full disk encryption and file based encryption. More details and some benchmarks can be found on the announcement and on the RPF GitHub PR.
Adiantum can be enabled as described in the Android documentation, but to make it short adding
to the current kernel config should be enough.
This would allow to finally have usable disk encryption on both external block devices, with cryptsetup/LUKS, and on home directories, with file-based encryption (fscrypt) on EXT4/F2FS.