For IMAP accounts, I see no sense in synchronizing ALL messages in ALL folders for offline access. It takes a lot of time, hogs Internet bandwidth and disk space and bloats up Thunderbird's profile folder, plus the fact that Google imposes bandwidth limits to Gmail access via IMAP and POP just makes things worse. Whenever I setup an IMAP account in Thunderbird, I always immediately go to Account Settings and turn off syncing of all messages, then restrict syncing to messages aged no more than 30 days. I then manually select which folders should be synced (Inbox, Drafts and Sent). I was primarily an Outlook user until Microsoft removed the option to download only headers after Outlook 2010, I think. If you're a mail hoarder and like to keep everything accessible offline, it's going to be a long long wait before Thunderbird syncs all your messages. If you have lots of huge messages and fast Internet access, you'll quickly exhaust Gmail's bandwidth limit long before all the messages are synced, then things will slow down to a crawl and you'll think there's something wrong with Thunderbird.

Whichever antivirus program you use, I strongly recommend adding Thunderbird's profile folder to its exclusions list and in some cases, turn off scanning of encrypted mail traffic to allow Thunderbird to work unhindered. You'll avoid a lot of problems with Thunderbird this way.

what spam and virus checker. My observation over the past 10 years is most problems are caused by antivirus/spam tools, not fixed by them.

So obviously the first thing is to see if you still see this in Windows safe mode with networking. https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-10-92c27cff-db89-8644-1ce4-b3e5e56fe234