Installing Debian 11 on existing LUKS/LVM drive
This is an update to by previous post for Debian 11.
If you want to install Debian on an existing luks encrypted device then the easiest way I've found is to use the network install image and boot into the "Rescue System" which contains cryptsetup from here you can unlock your device then exit the shell, got back through the menus to partition layout and continue as normal.
Once installed you will need to configure /etc/crypttab and run update-initramfs -k all -c