Canon EOS R8 lens advice

I'm going to be purchasing an R8 and am looking for a high quality lens to purchase that won't break the bank. I've been considering getting lens adapters, or just purchasing an RF lens. It's important to me to have a lens that I can have for a considerable period of time that's sharp and I can grow with it as a photographer. I'll mainly be shooting nature, landscapes, and some portrait/family style shots. Any suggestions would be very helpful!