I don't know if Bitlocker is setup already. I've until now only seen W11's language selection screen, have not have had time to start configuring this laptop 
What are the symptoms of Bitlocker is indeed already installed?
My biggest worry is that w11 configures all kinds of settings that make installing w10 and particularly Linux very difficult.
From your reply I learned that I can mitigate that through bios and Linux live usb. Excellent, thank you!