Thunderbird constantly showing that I have new messages, despite not having anything new in my inbox or any of my folders

On Bazzite, currently I'm running Thunderbird version 140.8.1esr. I only have one account set up in Thunderbird, which is my iCloud email account. I followed the steps in [https://www.macuncle.com/blog/add-icloud-email-to-thunderbird/ this guide] to set up my iCloud email account in Thunderbird, and it went very smooth. No matter what I do, no matter how many times I mark all folders as read, the icon in my dock ALWAYS displays a new mail notification. I've removed and re-added my account twice, and have uninstalled and re-installed Thunderbird from the Bazaar store. iCloud on the web also does not show that I have any new messages.