How to disable Apache manual or make it unreachable?

apache displays the manual pages accessible from any domain (/manual/en/index.html)… should I disable or remove the docs module? (apache2-doc)

I know that the docs module is optional, not sure why it is installed.

You should, if you don’t need this. You could use config search, when editing files manually to just disable it by hand:

… or disable it with a2disconf apache2-doc comamnd and restart your Apache afterwards.