Here is a fresh Canon EOS R5 review with focus on bird photography. A native RF lens and two big white EF telephoto lenses are used.
Jan Wegener reviews the Canon EOS R5 focusing on how well it suits for bird photography. He is tesing the R5 using the RF 100-500mm f/4.5-7.1L IS, and EF 400mm f/2.8L II and EF 600mm f/4L IS II lenses. In his words:
After all the gear reviews lately it was time to head out and do some shooting for myself with my favorite gear. With the Canon EOS R5, RF 100-500 & EF 4/600 L IS II, I headed on the road to find an elusive bird. Rumour has it that he can be found in a small fishing town! Will I find him and my other target species?
More Canon EOS R5 review stuff is listed here, for EOS R6 review stuff see here. The EOS R5 is highly regarded as a stills camera. In particular, the EOS R5 autofocus system seems to be huge leap forwards. User manual are available for download for the EOS R5 and the EOS R6.
Canon EOS R5: