Clarity is important on the topic of EF-S lenses on full frame, the camera(s) when the lens is installed can be placed into cropping/aspect ratio through the camera options. My R6MkII does it automatically, pretty nice feature.
Video, movie cropping mode concentrates the sensor's output, effectively turning the full-frame R8 into an APS-C camera. Stills, you have the ability to select different aspect ratios like 1:1, 4:3, or 16:9, or choose a 1.6x crop, especially useful when using RF-S or EF-S lenses
These were taken on an R6MkII using a EF-S 35mm f/2.8 Macro IS STM which I still own and use today. Yes the MP count is reduced but beyond that you will find very little degradation in image quality. Additionally these were captured in total darkness using a ULANZI L3 RGB LED and the focus was mostly dead on, some user error resulted in poor quality on a couple captures.
Quality is real good and the 11X14 prints I have on my wall look pretty darn clean. Using an R lens is always preferred but many EF/EF-S lenses work very well on all for the R series bodies. Know that high frame rates are also an area where the EF line on an R bodies is reduced.
