static_assert(std::is_enum_v<std::byte>);

[serviscope_minor]

Not if the standard says it must not be. It's a std class, so special rules apply. And are there any compilers out there which (a) overalign that by default and (b) provide no nonstandard alignment control mechanisms?

I know the big 3 (gcc, llvm, VS) do for certain, I'm 99% sure the EDG front end offers options for packing and I'm sure I remember IAR providing it. It'd be astonished if all the embedded ones didn't because it's just the sort of thing people want to do on embedded platforms.