It's an interesting question (as far as tax can be interesting!), whether patreon and other contribution/donations systems count as gifts, or income from your work.

I'm sure the tax authorities would like argue it is income, if you're making $8K monthly on patreon (e.g. Dwarf fortress creators).

Patreon seems to think it's likely to be income:

https://support.patreon.com/hc/en-us/articles/207477063-Taxe...

Which makes me wonder, is there some other way to aggregate donations such that they are gifts?

I think most tax departments will say they are gifts, but also that gifts are income.

And “give €5 and get a sticker” might make it a sale, making it subject to VAT, too.

In the US gifts are tax free unless someone gives you a large gift. Last I checked it was $10,000, but I believe it is around $18,000 now. Obviously this is large enough that few people care.

Gifts are always tax free for the recipient unless both parties fill out some additional paperwork. The annual tax exemption is currently $14k but goes up every couple of years.