The event window has no functionality for it to be minimised. Is it an icon on the Taskbar? If it's doing that, its very weird. If you rest your mouse on the Thunderbird icon on the Taskbar, does it split into the main interface and the Event window?

ignore post. forgot to quote question in my reply...

The event window has no functionality for it to be minimised. Is it an icon on the Taskbar? If it's doing that, its very weird. If you rest your mouse on the Thunderbird icon on the Taskbar, does it split into the main interface and the Event window?

Sorry for duplicate post. I meant to quote you in my reply and I can't seem to delete the first attempt. Yes, mousing over the Thunderbird icon on the taskbar splits showing the main calendar and the New Event creation window. Clicking the New Event window does nothing, nor does right clicking and selecting Move or Size. Restore, Minimize, and Maximize are all grayed out. The same thing happens when right clicking an existing event and selecting Edit. As I do this quite regularly, I am quite certain this happened after the Jan 8th update to 128.6.0esr

I was going to try the Thunderbird mobile app to see if I could create and share events but I have gmail accounts that use OAuth2 authentication method which is unsupported by tthe Thunderbird mobile app.