I am having the same issue. Just did a fresh install and am now locked out of the windows security app.
==EDIT==
I found this other post that resolve the issue for me. Here is the link Virus & Threat Tab Missing ??(Windows 11) - Microsoft Community and I have copied and pasted the answer below as well.
"I'm Kevin B., I do apologize for the inconvenience that you're experiencing right now, let me help you sort things out.
When did the issue started? Are there any other anti-malware software installed on the computer?
Kindly try to reset the Windows Security on your computer and check if the same issue appears
Using the Cortana Search box, search for Windows Security App
Right click on the resulting app and click on App Settings
Scroll down and select Reset
Follow the onscreen instruction until the reset completes
Restart the computer and check if the same issue appears
You may also run a system file checker to verify the integrity of windows system files on your computer making sure that there are no corrupted files on your windows.
Perform SFC Scan and Repair Windows Image
-This process will perform scan for any corrupted system files or integrity violation and will attempt to repair it along with the Windows Image.
- Open command prompt with administrator access
- Type each command below and wait until scan is completed.
SFC /scannow
DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /ScanHealth
DISM /Online /Cleanup-Image /RestoreHealth
Quick note: While the command is running, it's expected to see the process stuck at 20 or 40 percent. After a few minutes, the process will complete successfully.
Once you complete the steps, the Deployment Image Servicing and Management tool will connect to the Windows Update servers to download and replace any damaged files in the local image for Windows 10 as necessary.
- Close the command prompt.
Restart the computer once more and check again
Hope this will help and have a bless day!
Thanks.
Kevin B.
Independent advisor"