Ok, I just played around with a very old guide for RPI SBC and it still works, even including decrypting the root partition via SSH (dropbear)
Guide: keks24/raspberry-pi-luks: encrypt the "root" partition of the raspberry pi stock image "raspberry pi os lite" - Codeberg.org
Hint 1: DietPi-Drive_Manager | Add dm-crypt/LUKS support · Issue #3377 · MichaIng/DietPi · GitHub
Hint 2: Update-initramfs fails due to no compression support of kernel - #3 by LeFish
Tested on: RPi4B, Kernel 6.1.21-v8+
root@DietPi4:~# lsblk -o name,fstype,label,size,ro,type,mountpoint
NAME FSTYPE LABEL SIZE RO TYPE MOUNTPOINT
sda 3.8G 0 disk
├─sda1 vfat 128M 0 part /boot
└─sda2 crypto_LUKS 3.6G 0 part
└─cryptroot ext4 3.6G 0 crypt /
root@DietPi4:~#