Hi,
While not having this exact problem myself, I am using an office PC where I do not have admin rights, so installing some scripts is prohibited in some locations. As far as I know we lowly users should always have access to our documents/pictures/videos and desktop folders (although some companies go as far as to even lockdown the Desktop usage).
I have kept my 'User and System' paths (under the Configure User and Systems Paths) as factory standard.
The only thing that I have added is a new entry into the '3rd Party Plug-Ins' tab pointing to my /downloads/scripts folder.
All other scripts I run off a custom list that I created in a really handy 'ScriptList' script:
https://www.scriptspot.com/3ds-max/scripts/list-scripts-in-folder. This can be invoked from a single button on the standard toolbar. And if I'm migrating to a new version of 3DSMax (or if something breaks), I only have to create one button to get all my scripts back up and running. It's a very handy way to access lots of scripts at once:

It's very easy to set up, with one custom folder location (It should do four custom locations, but the script needs to be updated for 3DSMax 2019-> to work fully). As a work-around in situations like these, it works fairly well.
A windows update might well be your problem, considering that you should have full read/write privileges under your account level and windows group policy (if they have not been messed with), and I'll be watching this thread to see if it gets resolved. Sorry I could not be of more help.
Regards,
Darawork
AutoDesk User
Windows 10/11, 3DS Max 2022/24, Revit 2022, AutoCad 2024, Dell Precision 5810/20, ASUS DIY, nVidia Quadro P5000/RTX 5000/GTX760