That's a weird, new exception that you have there. In general, the differences between Java 8 and Java 11 are hard to work around, especially with regards to how they handle HiDPI monitor things.
I recently made a change to the way that I process texture lookups in the model's current directory, and when you're browsing models it points them to the default temp directory. I googled your problem and it says that folder you have there comes from when a Microsoft tech support employee remote controls your PC. Basically it looks like when my thing is trying to point the texture lookup code to the tool's temporary directory, somehow it got confused and went one directory above, and that directory contained this temp folder from your Microsoft tech support technician, which only the technician is allowed to access, not you, so it crashed my tool. But it points out a good problem that my tool was looking for textures one directory higher than it should have been.
I'm not aware of anybody else making model editors still in the Warcraft III community, so your best guess is going to be either to get a plugin like the one Taylor Mouse was working on to import Reforged models into commercial software like 3ds max, or to modify the SD Warcraft III models in the old format. There are several model editor tools for the old SD format that existed before Reforged, such as Magos War3 Model Editor, Mdlvis, the Prophet's War3 Viewer, Oinkerwinkle's tools, and others, as well as NeoDex for use with 3ds max.
Here's the link to the Taylor Mouse scripts:
Warcraft III Reforged - MDX format
Edit: as a note, I did some testing and I believe I have removed the cause of the weird error popup that you were seeing, so that fix should go out in the next version. I still don't quite understand why your 3D viewport scaling was bugged, though. I tested on my local machine running a build of the program with Java 11 when my Windows UI Scale was set to 200%, and for me the program still detects the 200% UI Scale on startup and fixes itself. But it's possible that maybe the way that I am detecting it does not work on all graphics card environments.