This is what mine looked like when I finally got it out.

What did you do to get yours out? Seems like cutting the bolt threads with a dremel until it's almost flushed with the plate and then drilling the rest out would be an approach I would take. Think someone earlier said they use an air hammer chisel and another, a multi-tool.

If I recall correctly I tore it apart from the bottom with pry bar, hammer and angle grinder. Then used the angle grinder to dig into the bolts from underneath until enough of each bolt was gone to pry it off. After reading how hard it was going to be on rust belt vehicles I was hoping the bolts would just break off and the part fall out but I could not get anything to grab onto the head of the bolt enough to get any movement out of them.

I recently faced this issue as well. All my TPMS sensors were bad (2007 4runner). Tech at the auto shop called said they could not get the spare tire down. Said the cable was frayed. They ask if it was ok to force I said yes go ahead.
I drove home with the spare in the rear cargo hold. They quoted $400 - $500 to fix the spare tire carrier. I said no thanks I can do this. Like others mentioned the bolts are very difficult to get to. I went to harbor freight and bought this Access to this page has been denied wrench which is low profile and flexible head and it is long for lots of leverage.

Because some of the bolts were so rusted I also had to buy these bolt biters. https://www.amazon.com/dp/B07PNS5QH4...t_details&th=1. The bolt biters worked awesome by the way.

Also a bit of Kroil spray seemed to help loosen the rust.

I then bought a new Toyota OEM spare tire carrier on ebay for $100. I spent more then I planned for to get it fixed but still saved a significant amount.