I have the R5, but have not been able to shoot any sports with it, however, with DSLRs, I have never used IS when shooting sporting events. I always turn IS off, even when shutter speed may only be 1/500. I handhold and use monopod, depending on lens. I use a monopod when I shot with the 500 and now 600mm lens. I handhold/use monopod (perhaps 50/50) when shooting with the 300 2.8 IS lens, but that comes down to being able to be mobile. And, when shooting indoors (mainly basketball), I always handhold with no IS on and shutter speeds gets down to 1/500. I just never needed IS for sports and I never liked how the motion looked through the VF with IS on. I found that few sports photographer around the net used IS mode 3, particularly when it was first introduced by Canon, but I never felt the need to do so. What's interesting though is I always have IS mode 3 engaged when shooting birds/wildlife with the 600mm lens on a tripod. I think because the IS doesn't kick in until the shutter is released, so I never see that IS motion in the VF, but never for sports. I've seen a few Youtuber's video where some have shot sports with the R5/R6. Ask some of them.
Hey, that might be a good poll to post for those who shoot sports.
Just One Man's Opinion...