A) On [developers.google.com...] it is cleary declared how to annotate dedicated mobile pages e.g. m.example.com/page or example.com/mobile/page (with canonical pointing to its desktop-sibling) and vice-versa (with link rel="alternate" media="only screen and (max-width:... pointing to the desktop's mobile-sibling.

B) Further, on [support.google.com...] its cleary explained how to use hreflang to declare language/regional versions.

However, sources in the web are contradictory when it is about bringing A and B together on dedicated mobile pages e.g. m.example.com/page

Which statement is true?
dedicated mobile MOBILE pages e.g. m.example.com/page...
1. ... do NOT need hreflangs because their canonicals are pointing to each desktop-sibling each containing the respective hreflangs
2. ... DO need hreflangs, each hreflang should point to one MOBILE language/region-sibling (including one hreflang for self-referencing)
3. ... DO need hreflangs, each hreflang should point to the DESKTOP language/region-sibling including one hreflang for self-referencing (also desktop version, i. e. the self-ref. hreflang in that case was identical to canonical)

Thank you and best regards, Stefan