I wish I could participate positively, but I honestly can’t think of any prep I’ve ever done that was enjoyable, unless we go back to junior high and focus on my kid self drawing fancy maps for AD&D. Even then, actually populating locations with monsters was hard.
I have a really hard time coming up with ideas away from the table. I have roped my non-gaming wife into brainstorming sessions so many times. Even highly procedural games, like PbtA stuff, have not proven easy for me.
I guess I just need more practice.