Heat prop, heat gun or heat hammer, throw ice on it. Repeat. Try to concentrate on the first inch of the prop from the hub, as that with any taper feature will be, and tapers can naturally lock in place!
Also take 1-part each acetone & auto trans fluid (ATF) & mix, raise OB & drip onto propshaft, as it is THE BEST penetrating fluid EVER! After or with the above, if still stuck, with rubber mallet, whack prop hub, then prop body, then wood against prop hub to push it off.
On one boat we backed off the prop nut a few turns, but still had the smaller cotter pin in it and we put it into reverse (in the water, duh, ... but didn’t want to lose the prop in 10‘ deep water, LOL) with boat tied securely to a dock, and with power in reverse, it knocked the prop loose.
You might see a counterbore in the end of the prop shaft, where that end was supported on a lathe. With the prop off and out of your way, you can use that as a ‘visual‘ in neutral, as you spin the prop shaft & see if that circle ‘wobbles‘.
