Hi Tom. I'm sorry no one's replied, and didn't want you to feel ignored.
Most likely, no one who has a solution has come along--yet.
I'm
definitely not that person, what with being a Linux-only, avowed windows hater!
But I do have some questions whose answers may help that other person(s).
various versions of Windows (Now on Win10 Pro V1909) and it would sync both ways. All of the sudden I can't get it to sync either way.
Did it stop right after an OS upgrade, or after some time? If the former, the obvious suspect is the new version of windows--but I get the feeling it's the latter.
So what else happened?
Around the time it stopped working, did you update anything else? You mentioned using an old version of Thunderbird--did you upgrade that?
Were any Google-related updates applied on your phone? That includes Android.
Did you install anything that could conflict with the sync function, like something that also syncs?
Hang in there! We'll try to help get it sorted out.