RSS feed from a site produces the error: The Feed URL "is not authorized."
I've been happily using the feed from https://babylonbee.com/feed for quite a while, but in the last few days, suddenly Thunderbird 91.10.0 (64-bit) gives me the feed "is not authorized" error. Previous solution https://support.mozilla.org/en-US/questions/1166672 isn't working for me - Lightning is no longer an extension, so I can't deactivate it. I'd remove the calendar function entirely if I could - I don't use it.
Going to advanced preferences and pulling up calendar.useragent.extra gives me radio buttons to select Boolean, Number, or String with a plus sign to add it. Adding one doesn't fix it. Setting to false doesn't fix it. Deleting the one I added doesn't fix it. Right click only gives me Select All, which highlights all text on screen and does nothing.
Most of my other feeds are fine, and checking the website shows the RSS URL has not changed.
Help?