It's rather ridiculous that this is the place I have to post this is, but apparently Stardock doesn't have proper customer support. They told me "post it on our Forums" so that's what I'm doing.
For a couple of months, Fences 3 has made it impossible to restart Windows Explorer, be it manually or if Explorer itself crashes. It returns a "MTweaker Error"

I have found zero online regarding this particular error. This has happened on both Windows 10 AND Windows 11.
Uninstalling Fences 3 solves the problem. Which means it's something connected to the program doing it.
I tried to instal the trial version of Fences 6 but, while it's slightly more stable than Fences 3 in this regard, the issue is still present, albeit less frequent. I don't need Fences 6, Fences 3 does all I need it to do, so I will need a solution for that one. It's been working great for years, there's no reason to start acting up now.
Below potentially relevant PC specs:
Intel i7-12700K 3.60Ghz
32GB DDR4 RAM
Windows 11 Pro 24H2, build 26100.4652 (although it also happened with the latest build of Windows 10).
Windows Feature Experience Pack 1000.26100.128.0
Asus NVidia RTX5090