like dogfood, a significant portion of the matter in dry cat kibble is of vegetable origin. It is of inferior nutritional quality to canned meat based cat food, but is the predominant form of sustenance for our feline friends.
Additionally, cats are significantly less picky in the sources of their protein intake. Insect based canned catfood would be suitable.
The REAL issue with veganism (as a mainstream thing) is that it places a heavy burden on the requirement for mono-culture. See the recent issues with Banana plants and panama disease. Similar issues could happen to the human food supply under aggressively mono-cultured crops. Historical examples: Irish potato famine, previous mass banana species extinction due to last round of panama disease.
There are measures that help to prevent this kind of problem, but most of them are not capable of producing crop yields necessary to feed a population of 7bn.
While a significant fraction of cattle fodder is human-grade consumable in nature, the fraction that is not is not inconsiderable. Cattle can eat things that would literally kill humans who tried it. (Fermented silage being a noteworthy example.)
https://en.wikipedia.org/wiki/SilageCattle represent an inefficient means of converting completely inedible (to humans) biomatter into a form that humans can eat. Insects could theoretically be cultivated on silage as well, possibly more efficiently-- however, I very much doubt that the "Yuck factor" would ever be completely eradicated short of there being a major global catastrophe.