Again - no browsers support jxl. Firefox "support" is only basic rendering of a few basic features. It's not just browsers, there is literally no software which fully supports jxl. And won't be for a long time.
Pretty much all compression algorithms work similar to JPEG. The newer formats only add even more crazy maths to the mix, but the base is pretty much the same.
Internally it will still read a whole word. Because the CPU cannot read less than a word. And if you read the ARM article you linked, it literally says so.
Thus any compiler worth their salt will align all byte variables to words for faster memory access. Unless you specifically disable such behaviour. So yeah, RTFM :)
The original WSL DOES use the Linux kernel. Which runs as a native NT process (there's a huge difference between NT and Win32 processes). But porting a Linux kernel into the NT binary is a maintenance nightmare, it's much easier to run the original in a slim VM.
The way it's been going lately is that the US is the only country which chose Trump. Don't worry about us, worry about yourself.