Yeah and they got Tatum under control through 2025 after which he has a player option he surely will decline (37M), so they gotta address that. Right now both Tatum and Brown are supermax eligible and since the 65 game rule comes in for All-NBA Brown takes a huge risk if he doesnt demand his bag now. Tatum at least has 2 consecutive All-NBAs which means he is automatically supermax elibigle next offseason as well (if I understand this stuff correctly).
So if Celtics would give Brown his bag, and then somehow find a way to extend Porzingis (they cannot use extension exceptions for a player who hasnt been in their roster for less than a year, right?), that would put them at a pretty high cap total with Tatum blockbuster deal looming on the horizon.