Studies of feces appear to indicate plant consumption was high. There’s also one I came across on Neanderthal diet 50k years ago that suggests they ate more plant stuff than previously thought. https://www.researchgate.net/publication/329486931_Dietary_f... https://link.springer.com/chapter/10.1007/978-1-4684-2481-2_...
This one says meat was an important component, but that fiber (only from plants) consumption was much higher than it is now. https://socialsci.libretexts.org/Bookshelves/Anthropology/Bi...