See https://bugzilla.mozilla.org/show_bug.cgi?id=1817705 and c. 6 for the More workaround.

Not ideal, but it works. Will have to re-learn my work flow and just get used it

Bug 1817705 says: "Convert to event/task is missing from the context menu. It is available on the More button though."

I have used Thunderbird for years and never seen the "More" button. A hint as to where I might find it?

Same page says that the problem is for version 113, and was resolved six days ago. Does this mean what we have now is how it's gonna be from here on out?

Bug 1817705 says: I have used Thunderbird for years and never seen the "More" button. A hint as to where I might find it?

It is in the tool bar on the top right corner when you have a message open, see screenshot. I hope this helps.

Bug 1817705 says: "Convert to event/task is missing from the context menu. It is available on the More button though." I have used Thunderbird for years and never seen the "More" button. A hint as to where I might find it? Same page says that the problem is for version 113, and was resolved six days ago. Does this mean what we have now is how it's gonna be from here on out?

The fix will appear in the next release version, 115.2, probably within a week.

Although highlighting the message I find the "convert to event/task", it doesn't work. When I click the option nothing happens.

This has now been fixed in Thunderbird 115.5.1 :-)