I have been using the TBsync add-on for quite some time without any problems but when I finally allowed TB to upgrade to Ver 102 that came to an end. After doing some fiddling around (i.e., disable/enable syncing) the calendar appears to have resumed syncing properly. I have done a bit of research but I'm afraid this turns out to be a fairly complex issue. For example, [https://github.com/jobisoft/DAV-4-TbSync/wiki/Since-Thunderbird-102,-TbSync-DAV-is-using-native-CardDAV-sync this article], seems to imply that TBsync is no longer needed to sync contacts but also suggests that it has converted to using built-in TB CardDAV capability which implies that it should continue to work. Also, TBsync includes syncing of Categories which can serve is an alternative to eMail (Distribution) Lists which apparently are never synced. At this point it would be helpful if I could find some documentation that elaborates a bit on how syncing without TBsync would work. This should especially include what servers it is known to work with.