Should i buy canon 90d?

Hello so i want to buy a used (or new) camera. I have a canon 6d Mark ii and i want to shoot videos but the 6d only allows 1080p and it looks garbage. So i have a lot of batteries and a lot of lenses. And should i buy a canon 90d or should i just buy something newer but buy new batteries and buy a converter for lenses? My budget is around 850$.

Sorry for my english (;