Adding mountains to the Exclude list does not seem to work, possibly because it is not sure what to put in the background. So, rather than using negative prompts, use positive prompts and say what you want in the background:
If you have a subject you like and just want to change the mountains, take the image into generative fill and remove the background and add a prompt for what you want the background to be:
This has become a joke among my students — we call it "The Machu-Picchu" effect (or maybe: "Riiiicoooolaaa"). It's bonkers.
I mean, sure — it's new and amazng tech, but between the fingers and the lack of detail and the mojntains, it's getting very cliche... almost like it's setting us up for a "spot the AI competition between amateurs and advanced users (or Firefly and MidJourney).
exhibit A + B: "man popping pimple" and "teenager picking nose"
I asked a friend to try simple prompts in MJ ... here's an A/B between FF and MJ with the prompt "latin woman playing guitar". Guess which is the FF...