I'm afraid there's no official content about that yet...
... but there's an official campaign which has some Lantanese in it ("Steampunk-Atlantis" close to Maztica and also disappeared to Abeir). I spoiled myself accidentally, because I play a gnomish Artificer from Lantan (that lived in Faerun since before the Spellplague) and stumbled upon some campaign info. I don't know any more about that and don't know whether those Lantanese give any interesting info about what happened exactly to their homeland. So I can't tell you any details, because I don't want to spoil myself anymore and don't want to spoil the story for anyone else, because it's a pretty nice campaign.
If you don't mean to play that campaign, maybe have a look into
I don't know if there's anything useful in it... there might be something tho... but again: I don't want to spoil anything for anyone here (me included).
Apart from that: Did you look into the Faerun Fandom?
The Fandom-Wiki and that official campaign are the only sources I know of regarding Maztica. I dug deep for my 383 year old gnome-character, but maybe not deep enough.
My DM/girlfriend (same person) told me that the designers might have something planned for Lantan and Maztica but I don't know if that was just a distraction maneuver to stop me from researching my character's background too much. So present Maztica pretty much seems like a yet to be filled blank spot on the map. Right now you can fill it (as a DM) with your imagination.
You could imagine it as a Wild West steampunk(ish) continent, but if official lore is of value to you, you may want to leave room to get retconned on this by upcoming official stuff.