- Selecting an existing LUKS partition for the / (root) mount point doesn't allow to provide an encryption password. Neither for the "Keep" nor for the "Format" option. The installation will later crash without an error.
- Selecting an existing partition in combination with the "Format" option allows to select "luks" as the "File System" which doesn't make sense and causes the installation to crash later on. Because the user can't provide an encryption password nor specify the actual filesystem (e.g. ext4) to be used within the luks container. Therefore this option doesn't make sense at all and should not be available in the "File System" dropdown.
- Selecting an existing partition in combination with the "Format" option doesn't allow to setup encryption for the root mount point or swap partition. The "Encrypt" checkbox is only available when you create a new partition but is missing when you want to format or reuse an existing partition.
- If you "Edit" a to-be-created encrypted LUKS partition again, you can't change the LUKS password anymore and the installation will later on crash. (I guess the previously setup encryption password is lost when you hit the edit button for a partition again.)