When it comes to crossplay, Larian has stated "Baldur's Gate 3 will support cross-save progression between PC, Mac, and PS5… Allowing you to transfer your saves between platforms and continue your adventure wherever you purchase the game."
However, Baldur's Gate 3 early access saves are not be carried across to the full game. You'll have to find your Baldur's Gate 3 save location and delete any early access save to play the full release.