So where is the tie between Thunderbird and Microsoft Windows?
I reinstalled Linix Mint 20 “Uma” and as a part of that process signed in to Thunderbird with my Outlook PW as my MS PW would not register. There, in the folder stack on the left was a folder named Notes. I opened the folder and my “sticky notes” were displayed. I used Notes software in Windows 10. Not wanting a connection to Windows at all, let alone in a Linux installation, as information flow is a two-way street, what’s left? Dump Thunderbird and Firefox from Linux Mint? Not use the MS sign-in credentials?
Thunderbird has no connection to Windows (other than it will run on Windows, as well as Mac, Linux, etc.).
But Thunderbird has added the concept of a "Thunderbird cloud account" or something like that, and I think it will let you authenticate using credentials from other non-Thunderbird identities, such as Microsoft, maybe Facebook for all I know. The idea is apparently to allow a sort of "Single Sign-On" (SSO).
CAVEAT: I might have that wrong, I don't use any of that consumer-level SSO shite, I don't trust it. Sounds like a great way to have all your various service identities compromised at once.
My employer uses SSO but that's all high-security services and I don't have any choice about that.