What are the actual parameters of an UD1 instruction?
https://www.felixcloutier.com/x86/ud

It says it's "0F B9 UD1 r32, r/m32".
But is it really only r32,r/m32 or also r16/rm16?
So basically full modr/m decoding and fetching in 16/32-bit mode, but no actual use of it (due to throwing #UD for the EU execution phase)?

So basically just like opcode 01 in both 16-bit and 32-bit operand and address size, but throwing #UD after fetching the instruction (so it will page fault on modr/m16 or modr/m32 if not present, but then #UD when it's fetched and trying to execute)?

Or more easily, 0F 19 HINT_NOP r/m16/32, but always throwing #UD on execution after fetching and trying to execute?