1
In the Windows Update settings section, below that update is a switch to 'Get the latest updates as soon as they are released', disable that setting.
2
Open File Explorer.
Go to the C:\WIndows\SoftwareDistribution\Download folder.
Delete the entire contents of the Download folder
Close File Explorer
Then, restart (not shut down) your PC and that should stop the optional preview updates including the KB5120998 installing on your PC.
You will still continue to get the normal monthly updates.