HI,
already checked Ideas, but what I'm, asking here is for an "official" support and documentation to already existing API (wondering why these APIs are not already documented in API Explorer . I don't think that is necessary an idea for this.
All supported Platform API endpoints are in API Explorer. If you've found hidden endpoints that aren't in API Explorer, they are unreleased, aren't supported, and shouldn't be used. The correct path forward is to request that they be released publicly via the ideas site.