You asked
Best telephoto lens for the canon eos r6 mark ii?
For most people on the R6 Mark II, I'd start with the Canon RF 70-200mm f/2.8L IS USM. It's a fast, versatile telephoto that handles events, portraits and sport well, and the body's low-light strength suits it.
If you need more reach for wildlife, the Canon RF 100-500mm f/4.5-7.1L IS USM gets you much closer to distant subjects. For a faster option with a shorter zoom range, look at the Canon RF 100-300mm f/2.8L IS USM.
If you want a lot of reach for less, the Canon RF 200-800mm f/6.3-9 IS USM is the one to consider, though it's slow at the long end.
For more on matching focal lengths to subjects, see wildlife and sport.
Written by Claude from this site's pages.