8.2 has broken the addon. Existing events won't open, can't create new ones.

Same error here. But I have found some of the Points That result the Errors:
GroupCalendar5/Libraries/MC2GuildLib/MC2GuildLib.lua in line 107 Change function GetGuildTabardFileNames() to new Blizzard API function GetGuildTabardFiles().
That was easy.

But for the second error in
GroupCalendar5/Libraries/MC2UIElementsLib/MC2UIElementsLib.lua line 737 :
Action[SetPoint] failed because[SetPoint would result in anchor family connection]: attempted from: :SetPoint
i cannot find a solution yet. But I know, That error results of this Changing:

Frame Anchoring
We added new restricted frames system that affects frame anchoring:
Frames that are anchored to a restricted frame can only have their other anchors set to frames within that same anchor hierarchy
Added new API in the Line API: Line:ClearAllPoints();
This will clear the anchors on a line and must be called to clear the restricted flag off of the frame.

https://us.forums.blizzard.com/en/wow/t/ui-changes-in-rise-of-azshara/202487

I hope That helps the Auto to fix the Errors.

BR Ralf