The cryptmethod tag is currently used in four questions, but seems a bit overspecific: although all four questions mention the
'cryptmethod' setting, only two of them are really about it. (In fact, the other two seem to be mistaken about what the setting actually does.)
The name of the Vim feature is "encryption", which covers these four questions and others which may not mention
I could do this myself, but wanted to check if others agree before doing so.