@Merlin5 - what Alan says is spot on, there is something off with camera/user settings here, I can see from the EXIF data in London Marathon 2021 (3) you are at F1.4 1/4000th and ISO800 and the background is blown out in places.
You need to look at why the camear was selecting 800 as the ISO, as the same shutter speed if ISO100 was selected would be 1/500th - which would give you a lot more headroom.
You have an Electronic Shutter available which will go faster than 1/4000th but they may introduce banding on moving subjects (this is common with a lot of ES sahutters, its down to the way the exposure occurs and the readout from the sensor), I don't know if your camera has a mode where it will shoot mechanical shutter to a particular speed and then shoot electronic shutter beyond that?
The traditional way of allowing slower shutter speeds at wide apertures would have been to use a 2 or 3 stop ND filter on the lens.