Previous reports have suggested that 75304 Darth Vader Helmet will be 721 pieces and 75305 Scout Trooper Helmet will be 567 pieces, making the Dark Lord set larger than the Biker Scout one. Another set rumoured to be launching alongside those other 18+ models is 75306 Imperial Probe Droid, which will be 538 elements.
The image above is 75227 Darth Vader Bust, a convention exclusive from 2019.
Star Wars: The Mandalorian is back on October 30, and this time around the LEGO Group will have the sets to go with it. 75292 The Mandalorian Bounty Hunter Transport was recently released and 75318 The Child will launch on the same day as the show (although some fans have found Baby Yoda already).
Rumours should be treated as such until official announcements are made by the LEGO Group.