OK. LUKS stands for “Linux Unified Key Setup”. You can take “LUKS disk” as being synonymous with “encrypted disk”, and “LUKS variant” means choosing to use an encrypted disk when you initially installed the software on the Librem 5 (although in this case I gather that that choice was made by Purism on your behalf), as distinct from choosing to use an unencrypted disk when you initially installed the software.
In view of that, the right answer is probably: Black screen after update
but for future reference
What it is: Jumpdrive allows you to mount the Librem 5’s internal disk on a host computer even when the Librem 5 won’t boot normally or is misbehaving in some way. (From there you would examine the contents of the disk to see what, if anything, is evident about what has gone wrong, and, where applicable, fix it.)
How to use it: Updated today , now phone won't turn on/start up