All good points but you were likely asked for encryption during setup, you just didn't notice (it's at the partition step). You are correct that it's impossibl

All good points but you were likely asked for encryption during setup, you just didn't notice (it's at the partition step). You are correct that it's impossible to do after the fact whilst the system is live. LUKS is also not very resilient. Bitlocker stores several copy of its headers in case of sector damage. With luks2 you're SOL.