If it's a two piece rim Norm, I would remove the outer half if it comes away ,once the tyres off I would usually give the alloy hub
at the back a few hits with a brass drift and hammer to try and shock it loose ,you could turn the mower on it's side and put the half
wheel in a bucket of white vinegar for a couple weeks or put the wheel on it;'s side in a big bucket with a little vinegar at the bottom
of the bucket so it works on that side of the wheel and put a drip feed on the other side of the wheel.
If you get the wheel apart you could try some heat ,I've seen a lot of broken alloy wheels when they get stuck on a shafts
probably best to soak the rust off ,but I can't see if it's rusted on or on a keyed morse taper.
When they are stuck tight if you can support the back of the alloy wheel then hit the axle through the centre they can come
loose but you would need the driveline out of the mower.
Cheers
Max
