I've done a few world building workshop and magic-system designs[1] workshop in a "nerdy-community centre" a few years ago. The community and interest for this is generally pretty small.

I was thinking about doing an interactive online version now that we're all stuck inside.

[1]: Someone in another comment mentioned designing hard magic systems, but there doesn't a whole interesting world of different magic systems out there: https://en.wikipedia.org/wiki/Hard_and_soft_magic_systems