You asked
Can I adapt the canon ef 16 35mm f 2 8l iii usm to canon rf?
I haven't covered that combination on cst1 likes cameras. The Canon EF 16-35mm f/2.8L III USM page lists only EF-mount DSLRs, and I don't have anything on RF bodies or EF-to-RF adapters, so I can't tell you whether it works with autofocus or how it performs on an RF camera.
The closest thing I have is the Lenses page, which covers adapting old manual-focus lenses to mirrorless bodies. That's a different situation from this one, so I wouldn't rely on it here. If you tell me which RF body you have, I can point you to lenses that suit what you shoot, such as the Landscape guide's wide-zoom advice.
Written by Claude from this site's pages.