You asked
Best portrait lens for the canon eos r5?
For portraits on the R5, I'd start with the Canon RF 85mm f/1.4L VCM. 85mm is the classic portrait length on full frame, and f/1.4 gives you a soft background without much fuss.
If you want the dreamiest look and don't mind chasing the fastest glass, the Canon RF 85mm f/1.2L USM is the one. For a slower f/2 option, the Canon RF 85mm f/2 Macro IS STM is still a solid portrait lens. If you want more room between you and your subject, try the Canon RF 135mm f/1.8L IS USM.
Whichever you pick, remember that light beats gear. Find a window and turn your subject toward it.
Written by Claude from this site's pages.