Use case diagram: include or extend?

Question

UML

This question in a different form is often found, a lot of things are googled on it, but I still could not understand - which is true? If there are several actions and, in principle, some of them will definitely be performed. So all of them - what? include? Or generalization?
Some sources write: if the action is not necessarily performed, then this is extend. Others - if at least one of the actions is required - definitely include.
In general, below is the diagram. Which one do you think is correct? It implies that the user can edit the letter, i.e. edit body AND/OR topic.

Another example. Unambiguously, "overwrite" is an extension of "add". But here's the "add" and "remove" themselves - include "file management" or extend or generalization?