Mind mapping is a great tool for making connections between ideas, and it's especially good for visual learners. It's not for everyone, and it's obviously not required. The "What if" exercise is also a excellent brainstorming tool, and the tool I personally use most often. I can brainstorm in the shower or the car with dictation tools on my phone, or I can type/swype in front of the TV while my husband watches football or anything else I can zone out. It usually looks/sounds something like this:

What if the MC did the thing?
But, wait, no, that doesn't work because reasons.
So maybe instead they did the other thing?
Ooh! What if Minor1 did the thing while MC was unable to do the thing...

Etc. Sometimes I just leave it like that and plan to revisit it later. Sometimes I pin down something I want to use and I'll add that to the bottom, delineated so my eyes can jump to the conclusions faster:

Final: Minor 1 did the thing while MC did the other thing, since MC was unable to do the thing.

And sometimes I have an EPIC breakthrough!! When that happens, there's maybe a 50/50 chance I decide later that it's not so epic or won't work because of other things I've decided, but the other half of the time it stays epic. 😁 And those are the moments that make writing - and planning - rewarding.