Syncing only occurs after you open the application. It may take an extended time for the details to update, depending on the mail server, the internet connection speed and other software like antivirus that may slow updates to a crawl.

Syncing also only occurs is your account is IMAP. POP accounts do not sync, only download mail

I understand the syncing process but I never had this problem before. I've been using Thunderbird for many years with my IMAP email account. After opening the Thunderbird application and letting it run for awhile I still had 85 emails showing as not read yet when accessing my email account directly it only showed 17 unread emails. Internet connection speed is fine Thanks for your input anyways

Do you have antivirus scanning your email? Might pay to try it without.

Right clicking the folder, selecting properties and then repair can fix indexing issues. This might be an indexing issue.

No 3rd party antivirus software. Like I said I never had this problem before and I have changed nothing on my PC except for the normal W11 updates. Very frustrating. I will try right clicking on the folder as you mentioned. I'm assuming you mean the Thunderbird inbox folder on my PC.