Can't run Windows Update: error 0x800f081f

My system has been stuck in this for ~2 months. Windows Update states I've missing security and quality fixes with the following message:

There were some problems installing updates, but we'll try again later. If you keep seeing this 
and want to search the web or contact support for information, this may help: (0x800f081f)

After a lot of Googling, I've tried a few things to fix it with no luck:

sfc

sfc /scannow

this always returns:

Beginning system scan.  This process will take some time.

Beginning verification phase of system scan.
Verification 100% complete.

Windows Resource Protection did not find any integrity violations.

DISM.exe

I run:

DISM.exe /Online /Cleanup-image /Restorehealth

which always returns:

Deployment Image Servicing and Management tool Version: 10.0.19041.329

Image Version: 10.0.19041.388

[==========================100.0%==========================] The restore operation completed successfully. The operation completed successfully.

Manual Install

I've downloaded the update and manually install them, but they always fail. The dialog simply says "Some updates were not installed" and then lists them. No other additional information.

Troubleshooter

I've tried to run the Windows Update Troubleshooter, but it says it "No recommended troubleshooters" right now & I don't see a way to force it?

.NET Framework is enabled

I've checked that the .NET Framework is enabled (as instructed here, step 5)

Next steps?

Any suggestions on what to try? I'm a recent convert from the Mac, so a bit of a fish out of water in trying to figure out what's going on. Any help is appreciated.

Error Code 0x800f081f means CBS_E_SOURCE_MISSING.

Perform a in-place upgrade (Repair Installation).

Have you installed a 3rd party Antivirus and/or a Firewall Program?

When yes, go to Step 1. When not, go to Step 2.

Step 1: Uninstall the antivirus/firewall program use the removal tool of the respective manufacturer of the antivirus or firewall program also.

A list can be found at the link below:

https://www.dell.com/support/article/de/de/debsdt1/sln208651/utilities-to-completely-remove-antivirus-software?lang=en

Step 2: Then perform a Windows Repair Installation.

https://www.tenforums.com/tutorials/16397-repair-install-windows-10-place-upgrade.html

Friendly greetings

Sorry for any mistakes. English is not my native language.