I've recently been spending some time trying to shoot fast-moving things with a variable-aperture zoom. This is annoying; not because I have any real problem with the variable-aperture nature of the lens, but because of a usability issue: In Av or M mode I dial it to f4 (the maximum). Then I zoom in and it gets changed automatically to (say) f5.6. Then I zoom back out and it remains at f5.6 until I adjust it again.
Is there any way, on a Canon R-series camera, to tell it "I always want the widest aperture that is available at the current focal length"? This seems like an obvious and useful function, but I'm not aware of any mode that does it (except perhaps for "portrait" auto settings on older / cheaper models)