Facebook groups and Discord are both pretty horrible places to go. Discord isn't set up to have archival information easily available and Facebook groups are only marginally better.Aside from the usual forums like this one, there are Facebook groups and discords if one is looking for an alternative to Reddit.
If I were starting fresh today, I'd point new DMs at Matt Colville's Running the Game videos. Heck, I binged them all during lockdown and I found them useful, despite years of play.
And not to pile on, but my dad, who's toying with becoming a DM (they grow up so fast!) purchased Return of the Lazy Dungeon Master first thing.