The "path" gives your operating system a reference to the needed files. In this case, whenever you type in "pip" as a command in your command prompt, it knows where to find "pip" so it can complete the instructions, "install scipy" for example. Same with python; if you wanted to run a python script from the command prompt, you'd only have to navigate to the directory of the python script then type "python filename.py" and it will use python to run the script.. . . PATH (whatever that is) . . .
When you install Python, I think it asks if you want it to setup the paths for you. Double check that you have this setting flagged in the setup. Try running the installation for Python again and make sure to run the installation as administrator to ensure it has the proper rights to create those paths (it may not need them, but just in case).Might still be a part of the problem of PATH
Edit: Actually, this GUI program is probably depending on that system path to call the ESRGAN script using Python. If the path isn't created, I believe it will fail. I would go ahead and fix the paths just to be safe and rule out any potential failure modes.
Did you install the other runtimes from step 3?
3)Install the other runtimes (from "runtime" folder - default options)
ImageMagick-6.9.10-14-Q8-x86-static.exe
vcredist_x64.exe
vcredist_x86.exe
vbrun60sp6.exe
Another question: Did the upscaling program give you a specific error message when it failed?