Comment by leptons
I suggest starting with 8-bit MCU assembly, like AVR or PIC, or even something like 6502. It's very easy and cheap to get started, anyone with an "arduino" could write assembly for it, and 8-bit assembly is still relevant for very low latency real-time systems, or cheap simple solutions. You can do a lot with 10MIPS 8-bit MCUs that has a bunch of easy I/O peripherals. It's easy and accessible. I think 32-bit assembly is less common because C/C++ is usually the right tool for most of the jobs a 32-bit CPU would be used for.
I think 6502 is a very good and accessible assembly language for beginners, and I've done a decent amount of work around it