And a Google on "where is .net framework on my Windows 10 PC" tells me it is in Apps and Features - which I had already assumed - and I look again it is still not there.
You can try the System File Checker Tool sfc and the dism tool from microsoft.
Close all programs and open your cmd console as an Admin, and start with
sfc /scannow
After that go further with the Deployment Image Servicing and Management Tool.
Run dism in this order
dism /Online /Cleanup-Image /ScanHealth
dism /Online /Cleanup-Image /CheckHealth
If there are errors use this command for correction
You can try the System File Checker Tool sfc and the dism tool from microsoft.
Close all programs and open your cmd console as an Admin, and start with
sfc /scannow
After that go further with the Deployment Image Servicing and Management Tool.
Run dism in this order
dism /Online /Cleanup-Image /ScanHealth
dism /Online /Cleanup-Image /CheckHealth
If there are errors use this command for correction
Microsoft Windows [Version 10.0.19043.1288]
(c) Microsoft Corporation. All rights reserved.
C:\WINDOWS\system32>sfc /scannow
Beginning system scan. This process will take some time.
Beginning verification phase of system scan.
Verification 100% complete.
Windows Resource Protection found corrupt files and successfully repaired them.
For online repairs, details are included in the CBS log file located at
windir\Logs\CBS\CBS.log. For example C:\Windows\Logs\CBS\CBS.log. For offline
repairs, details are included in the log file provided by the /OFFLOGFILE flag.