We’ve seen how Blackbeard has just been chilling on his island, but knows exactly what’s going on.
As of now, the Big Mom Pirates are approaching Wano Country. Alongside Big Mom, we see many of her children like Smoothie, Perospero, Oven, Daifuku.
The glaring absences here are Cracker and Katakuri, who likely had to stay behind due to their wounds.
Blackbeard has shown himself to be an expert planner and a master at orchestrating manipulative schemes provided he has a sufficiently advanced period of time to prepare. I think Wano will be no different.
We’ve seen how Oda likes to draw parrallels between pre and post timeskip (e.g. Alabasta=Dressrosa, Enies Lobby=Whole Cake Island). Wano will be Impel Down and Marineford combined.
Now what did Blackbeard do in those arcs? Off-screen, he invaded Impel Down to recruit extremely powerful “Level Six” prisoners to strengthen his crew and then showed up at the end of Marineford on screen when everyone was injured already to steal Whitebeard’s Gura Gura no Mi devil fruit.
It’s a common theory that Blackbeard will show up at Wano at the end of the war, but I think beforehand he will invade Whole Cake Island!
Off-screen, Blackbeard will invade Whole Cake Island, kill a loved character in Katakuri (adding to his villainous character), take what he wants (the Road Poneglyph) much like he did in Impel Down.
Then he’ll show up in Wano at the end of the war where every one is weakened, take Kaido’s Zoan devil fruit (like he did to Whitebeard in Marineford) and take the Poneglyph there as well, giving the Blackbeard Pirates a headstart on finding Raftel.
*Theory by AzyT___1