Update. Spoke with a friend that lives far enough away he can't take a look at it. He knows I have been building computers for 20 years, repairing other appliances, and doing my electrical for years as well so he said to go ahead and test it with it jumped past that thermal fuse in the front bottom, but to keep an eye on everything. Was working perfectly fine, then quit again. Tested it with a no-contact tester to see where current was and was not, and when I bumped the bundle of wires, it kicked back on again. Would do this every time I pushed a little down on the bundle of wires running between the access to the control panel and the fan housing. This was with the bottom fuse jumped, so I tested it with the fuse in again and it worked the same, so I assume the bottom fuse was actually fine? Haven't had a fuse that would fail a continuity test but allow function before, but then again I'm not used to thermal fuses, just current fuses.

Because I couldn't access all the connections to check for loose wires further in beyond the power supply board, I took the outside shell off and checked connections. Got to another thermal fuse I wasn't aware of attached to the side of the mount for the magnetron. The plastic around the clips attached to this thermal fuse were bubbled up and burnt, and seemed to be loose when the main bundle of wires were pressed a little to add tension. Pushed these clips further on and re-tested, with everything isolated and plenty of room between it and me of course. Obviously would replace the clips, but wanted to test if that was the issue before tearing into it more to get at that fuse mount. With them seated and trying to run it, it arced off the fuse to the magnetron shell and tripped the breaker. Got into it to pull that fuse out, clipped the wires back further than the melted insulation and plastic shell around the clip, stripped the wires back and attached them to jump it, and the microwave works perfectly fine with no intermittent cut-off. Looks as if that #110 thermal fuse is the same for both the bottom front fuse and top fuse by the magnetron, and it blew that fuse for sure when it arced. The housing of it was brittle, whether that was from the arc or part of the issue in the first place, I don't know.

Will get that fuse ordered since I'll have to replace it anyway now, and will see if I continue having any intermittent cut-off with that fuse replaced. As mentioned, there doesn't seem to be any issue once I made sure the power supply board connectors were well seated for sure and had the wires for the top thermal fuse jumped rather than a fuse on them. Still a little iffy on messing with any other component of the electrical, which is why I stayed well away from it when testing after seating those bad fuse connectors (glad I did for obvious reasons). I am used to lower voltage electrical, and have a healthy respect for higher voltage, so I am careful not to touch anything energized and discharging before reaching in to work on anything.