Before last week's trip to Maine, I picked up an RF 100-400mm f/5.6-8 IS USM lens at Best Buy. I have until October 24th to return it should I so choose. At this point I think I will hang on to it.
It's a value lens for sure but it does the job when I want something longer than 105mm. Diffraction doesn't start to soften images until past f/11with my 20MP EOS R6 body and it's diffraction limiting aperture of f/10.6. I'm not sure how I would like using the lens with the EOS R7 body and it's diffraction limiting aperture of f/5.2.
Here are some images with the lens from Maine along with the current bag setup in the Think Tank Photo Streetwalker, which weighs about 11 pounds with this gear, and the RF lens lineup.