Edge changes my eMountain bike activity type to eRide, why?? And how to stop it?

I suspect that the Edge 530 does not have the sub sport defined, based on its age, so just attributes it to the parent sport classification.

FIT files use a sport and sub sport to classify activities. The sub sport is optional. Not that this helps you, but does explain what is likely happening.

e_bike_mountain is a sub sport of e_biking.

I think the problem is, it 'detects' I'm riding an eBike and it overrirdes eMountainBike with eBike, WTF stupid idea....

how to disable 'auto' eBike detection/overriding ?

Is this in Garmin Connect?

edge 530, my settings ^^

And when I'm saving it's already changed

I can confirm, finally works as expected.