I went and bought a $50 push mower from Facebook Marketplace today...and then had a brain fart moment and realized what's wrong with my old one.
When I tried to start it without the blade on, I broke the flywheel key. You can't start a lawnmower with the blade off and I had forgotten this. That's why I thought it was seized, and was able to free it up by hand.
I was getting spark and gas so couldn't figure it out, but this is it...the timing is off because the key is broken. An easy fix as long as you have a flywheel puller, which I do, and probably a $1 part.