Hey.
I found how to fix the issue. I had same issue tried alot of things and nothing worked untill I looked up this.
Type Run in search then services.mscand then try to find Windows Update.
If you can't find it on your list then this is what cause the issue.
To get it back I followed instructions in this link - >
https://www.tenforums.com/tutorials/57567-restore-default-services-windows-10-a.html
Find the Windows Update reg file download it from the page. then run it and restart your pc.
After restarting type Run in search then services.mscand then try to find Windows Update. right click properties start up type -> automatic and hit apply .
After that you should be able to run the .NET Framework 3.5 installation and it should install... at least it did for me.