I am not sure this is really about Installation and updates, but none of the others seemed to apply. This is the second major issue I have had since upgrading to 128esr. I am really inclined to go back to 115. The only way to get my Calendar to display properly is to leave that tab on top when I quit, so it's on top when I launch Thunderbird. If I don't do that, I cannot get my appointments to display and I get no notifications. The Calendar is blank and stays blank, even though it claims my Home calendar is not hidden. I did try hiding it and unhiding it again, but that didn't help. I do not have any Calendar-related add-ons. It's severely annoying. It means that if I forget to leave the Calendar on top, I have quit, re-launch, and re-log into all my e-mail accounts (I've got a bunch). Could someone please find a better solution for this? I am using Thunderbird for Mac on a MacBook Pro, 13 inch, mid 2012 running 10.15.7 (Catalina), which is the best the thing can do. Only tell me to upgrade my hardware if you are offering to pay for it yourself. Thank you.