So I searched for "single page" messages on the forum and found dozens of
messages ! I guess I used the correct keywords this time :).

To sum things up, there's no solution. HTTrack doesn't support "single page"
archiving and there's no equivalent to the "--page-requisites" wget option.
People have been asking for it for years, since 2001 ! However Xavier Roche,
HTTrack's main developer, replied to some of the first "single page" messages.
So I advice to read its answer to message 8229. His solution is to use filters
until the feature is implemented. But filters don't work well if you plan to
archive pages you don't know the contents. You can't just specify filters for
files that don't have an extension or you don't know anyhing about for
example.

My advice is to use wget until HTTrack implements the feature. I hope people
will find this "message in a bottle".