The Fn and Carl keys can be switched in software. I have a work-issued Lenovo with a similar layout. They can be soft-swapped in the BIOS. There’s also a desktop utility to do the same but I don’t know if they have a Linux version of it. I totally agree, the physical layout is annoying but it has a simple fix.

It’s still E2EE, as far as I know. Meta could always remove that feature but until they do, I’d consider it a safe and private messaging platform.