I recentlly discovered that Microsoft OneDrive, Phone Link, Microsoft Store and Windows Update had stopped working, all claiming I was not connected to the internet. This wasn't true, as my browsers were still working. I contacted Microsoft Support who found that their Quick Assist app couldn't connect.
Microsoft suggested a clean boot, and when I did this with Kaspersky Total Security V 21.3.10.391 running the problems persisted. After pausing the Kaspersky protection, all the Microsoft apps worked correctly.
Searching through the Kaspersky Forum I found this thread which provided a fix by Friend https://forum.kaspersky.com/topic/ms-teams-only-works-when-i-disable-my-kaspersky-35859/
This fix solved the immediate problems, and all the Microsoft apps worked correctly with Kaspersky protection running.
Reading further in the thread I found that I should have installed Kaspersky Plus to replace my Kaspersky Total Security. I have done that, and everything is working.