I am not using LVM for performance reasons.
I created my LUKS encrypted volumes manually in terminal before starting cnchi. They were mapped to /dev/mapper/sda2_crypt etc. after using cryptsetup luksOpen on each of them.

Problem: cnchi doesn’t find nor list these containers at all, and instead displays the /dev/sda2 partitions (it does see the LUKS header though). So I can’t install the system and select various mount points using my already existing encrypted volumes (which I created with --cipher aes-xts-plain64 --key-size 256 --hash sha256 --iter-time 2000 --use-urandom for example)

Suggestion: in the advanced setup, either add a new box after selecting LUKS encryption, to add custom parameters to cryptsetup (below the passphrase prompt box)
OR
detect volumes mapped in /dev/mapper (as they are visible for people who use LVM)