Thanks for the reply Dave67, on the right track.
Using Option 1; I cannot find "Let apps on my other devices open apps and continue experiences on this device from on to off".
Using Option 2; "Email & Accounts> Accounts used by other apps" shows my e address with " Microsoft account All Apps can sign me in" I have no remove button on option 2, only a "Manage" option that takes me eventualy ,chasing manage options, to
Sign in to your Microsoft account where I am offered to find my phone and other helpful things.
I am retecent going further including option 3, I have been bitten by making wrong changes involving Microsoft account, ultimately involving arbitration as to my identity. A hassle beyond perhaps resurecting.
Any other Ideas to get the Option 2 remove button?
Using auto updated Win 10 20H2 OS build 19042.985 Experience pack 120.2212.2020.0.
and, incidentaly, Mozila Thunderbird e mail app.