That is what happens when the mower is not maintained properly and he wheels do not come off every now & then for greasing the axels.
It has rusted solid onto the axel
If you have access to an oxy set or an induction heater then you heat the wheel hub red hot then tap it off .
This requires repainting the wheel
I use a pair of scissor jacks between the wheel & the body
The axel has 1/8" to 1/4 " movement in & out so the jacks just take up this movement plus put a SMALL amount of pull on the wheel
Then I use an air hammer / chisel on the axel while pushing very hard so the point is always hard against the axel. a bit of heat and a lot of penetrating fluid.
When the wheel moves a little then it is steel wool the clean the axel , penetrant , tap the wheel back on and repeat as necessary, tightening the jacks as the come loose and drop down
Some wheels have taken more than a full day to shift
Do not use excessive force pulling the wheel out as it will come out, complete with the axel as it is only held in with a snap ring or E clip and then it is a major repair to split the box , find the broken parts and close it back again.