You did the 153G update thing to yourself, When you Verify the MSFS 2020 files with Steam, it pretty much wipes all the content the game downloads after. Now you know so don’t do that in the future if you want to avoid redownloading the entire game, yet again.
As for your reboot. I had something somewhat similar happen the other day for the first time when clicking on the world map. I was somewhat pointing the blame to my newer 3090 in my system as it is known to pull 450W~ on a moments notice and since VSYNC doesn’t seem to work in the menu, well that can cause a spike for sure. You have older hardware and I am curious how old your PSU may be at this point? Even with a 4th Gen Intel and a 1080, your 660W PSU may possibly be getting near the end of its life if its anything close to the same age as your 4th Gen CPU. However you may also want to take a look in your motherboard bios and check to see if you have any sort of options or “Surge Protection” within the power or cpu settings as this may also cause the PC to shutdown/reboot due to a spike in load that it thinks is out of spec. I actually had mine turned on and since disabling, so far the reboots have subsided so far (Also happed in CP2077 so it wasn’t just MSFS for me.)