At the risk of sounding like a complete noob... "how do I actually use the updater included with the download of thunderbird 91?"
I downloaded and extracted the TB91 archive from https://www.thunderbird.net/en-US/ . I see an updater patch, but I do not see a basic "Read Me" to explain how to use the updater patch.
sudo chmod +x updater, then
$ ./updater , but get errors.