I watched this GDC talk recently about practical creativity: https://www.youtube.com/watch?v=zyVTxGpEO30

I like his perspective that creativity = using an existing pattern in a new context.

You can be more creative by first consuming lots of different patterns in all sorts of contexts (e.g. playing lots of games, and also reading and experiencing lots of topics unrelated to games).

Then you try all the different permutations of patterns in your mental toolbox. Kinda like how the sibling comment rattled off different what-ifs.

EDIT oh and oblique strategies might be helpful to come up with variations on an existing theme: https://stoney.sb.org/eno/oblique.html