Thunderbird TbSync plugin not compatible... but compatible?

OS: Ubuntu/Linux 20.04 Thunderbird: 102.2.2 My calendar stopped working, and it appears that the reason for that is that the TbSync plugin is not compatible with TB 102.2.2. No updates of the plugin are available. However, when I click on "more information" I get a message saying "The add-on “TbSync” seems to be maintained and is compatible with Thunderbird 102.". What do I do? I must have a working calendar in my e-mail app. So far I tried to reinstall everything, which took quite some time, but this did not help. I considered going back to an earlier version of TB, 102.1 maybe, but apt policy thunderbird does not list any versions between the ancient 68.7 and 102.2.2.