First of all thank you! And second I never knew this. Having only switched to mirrorless this year I must admit it's not something I've really thought about. I've never noticed it on my Fuji X-T4, though. The lowest I can reliably go is about 1/30th, anything after that it's either pot luck or I claim the blurriness is what I intended and call it an arty shot.
This is 1/30th at 100mm, with both lens and IBIS on. The Fuji 100-400 apparently auto detects panning. I've never found it to be a hinderance but other lenses and cameras might be different.
British GT Donington Decider 2022 by
Richard Crawford, on Flickr
The speed of the car matters as well. You'd get similar blur at a higher shutter speed if the car was going much faster, its all relative.
This was taken at 1/4th which is as slow as I've ever gone and got something even remotely sharp(ish)
British GT Championship Oulton Park 2021 by
Richard Crawford, on Flickr