If the piston does not move when the flywheel is rotated, you have major damage, and the engine is very likely not worth repairing. It will likely be less expensive to replace the engine, or replace the entire mower, than it would be to attempt to fix this. It sounds like the blade struck something solid, and the connecting rod broke, so the piston is no longer connected to the crankshaft. If you know a local small engine mechanic, you might be able to get this fixed for a reasonable amount.

Not the best news. But just so I'm clear, should I be able to see movement through the spark plug hole for this model engine, i.e. the "plate" my screw driver touches is the piston head AND turning the flywheel should result in the piston head's movement? While this may seem obvious, I just want to make certain there isn't a part of this I didn't accurately describe.

Its hard to see a piston head, looking through the hole where the spark plug goes. If you stick your thumb over the spark plug hole, and have someone rotate the flywheel for you, you should feel some air pressure against your thumb. That would be a crude compression check. You could bend a piece of coat hanger wire to stick down into the cylinder, so it has to touch the piston head, and then repeat the test, turning the flywheel. The piston has to move, up and down, as the flywheel is turned.

I have the same issue on a 8hp tecumseh. I believe it's a hm80 non over head. So I shouldn't be able to see anything moving through plug hole? To verify piston is moving I would need a coat hanger??
If piston wasn't moving how would motor run?

It wouldn't.

If you have someone pull start the engine while you hold a finger over the spark plug hole, the pressure should blow by your finger if everything is operating fine. Since it is hard to turn over, suspect major engine damage. Pull the head off the engine and have a look. Any scoring in the cylinder, scrap mower and buy a new one.