If it’s a niche it should probably have a dedicated community for it: e.g. c/cooking@lemmy.world

Personally I did like the button sewing post, maybe that is generally useful enough that everyone should know. But I’m already in a few repair/DIY community that never get enough posts, and I’ve just found a ‘Sewing, Repairing and Reducing Waste’ one where it’d fit too.

Maybe it could be tolerated but should have a tag like [NICHE] in a title and a recommendation that OP should cross-post it as a way to promote/ support the other communities.