I've changed babies in the F-lavatory on a UA 737-800, a UA 737MAX8, and possibly a UA A320. I think there is also a changing table in the very back Y-lav in the A320 as well. I'm less sure about the A320, 'dad brain' is a real thing and the babies have had a negative impact on my memory.

And before you give me grief about having babies up front, know that both of them just want to stare out the window and quietly snuggle - they are excellent plane kids! We got lucky.