Hi and welcome to the forum:
I have the same cameras myself and I am a wildlife photographer. As always much depends on your budget, but making the assumption that it is enough, I will suggest two lenses to you for wildlife. First I will say that one can never have too much focal length, but a fixed focal length lens can be challenging, as you are not always going to be in control of the shooting environment and the subject - in fact, very often not. For that reason I have always favoured a zoom lens for this work.
Essentially, there are two lenses I would suggest, and I do so owning both.
1. RF 100-500L I IS USM. This is a fabulous L series lens, and has dual nano-USM focusing motors, making it blazing fast to find focus. It has excellent optical quality across the focal range.
2. RF 200-800 IS USM. While not an L-series, it is well built, with some sealing, is amazingly light for the focal range and has excellent optics. Don't be put off by the max aperture of f/9 at the 800mm FL: remember the longer the FL the shallower the DoF and both bodies we have are fine to work with higher ISO values. If you go to the menu at the top and select Gallery > Share Your Photos, you can search for references to images take with each lens.
As to portraiture, I honestly think you are well covered by the zooms you have, but if you wanted a prime lens for that, you could consider the RF 100 f/2.8 Macro lens, which is also a fabulous portrait optic.
cheers, TREVOR
The mark of good photographer is not what they hold in their hand, it's what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
