I wonder whether oak gall ink is vegan. The larvae of the gallflies (actually wasps) that grow in oak galls emerge as adults in early summer, according to the Wildlife Trust, leaving the gall mostly intact. Thus, theoretically, it should be possible to make oak gall ink without harming any animals. It would still be an animal product, but produced only from by-products of a wild animal. But then again, perhaps change…
Interesting question. First I'd say veganism isn't a monolith, so opinions will probably differ on the matter. For instance, there is some debate about whether figs are vegan since they are pollinated by fig wasps which then die inside (but are completely absorbed by the fig). I think galls fall into a similar space, but perhaps are less of an issue since they are nominally rid of the insects once they are harvested (though I somehow doubt it can be guaranteed to be completely larvae-free).