It's not uncommon for pot shafts to seize up especially in a hot humid climate, even worse if you live near the sea. If the shaft and bushing are alloy it's even more likely to happen if not used for a long time.
Alloy against alloy is prone to lockup as alloy corrodes rapidly if no lube. If the lube dries out then corrosion grows rapidly and locks up the bushing.
The better quality pots use brass shaft in alloy case.
Just ask a fitter why you use dissimilar metals when making bushings and shafts.

I'd just remove the knobs then get a can of RP7 or WD40 or what ever brand you have in your part of the world which is penetrating oil, some times marketed as water dispersant.
Leave it soak for an hour and then gently but firmly grab the bare shafts with pliers and see if they move. You have to be careful with slotted shaft and not to destroy the spline, if they are D shaft then less chance of messing it up.
I've saved a few pots over the years but sometimes they are beyond repair.
But give it a try.
As mentioned ,,give the case some heat as well.
Phil.