Summary
Despite having some promising moments early in his career, Carter fell out of the rotation in the playoffs with the Suns in 2021, and after being traded to Brooklyn was waived during the '21-'22 season in order for the Nets to facilitate some trades. Carter then signed with the Bucks, and received some decent playing time, but wasn't fully trusted to be a consistent part of the rotation in the playoffs, even with Khris Middleton injured.

Carter is a combo guard that is best served defending point guards but playing off the ball on offense. He works really hard on defense, and slides his feet well to stay in front of ball-handlers. While his steal rate was low in '21-'22, he had a high steal rate each of his first three seasons, so it's likely he can get back to his disruptive ways and force some turnovers also.

Carter is a solid 38% shooter from three, but he isn't a playmaker and his field goal percentage at the rim is near the bottom of the league. Therefore, Carter's role on offense is pretty clear, and that's to make open spot-up threes. If he can do that, and hopefully expand his game enough to be able to attack hard close-outs and either make a play for himself or others, he could stick around in the league.

Carter will already be 27 years old by the time the '22-'23 season begins, so Carter needs to start showing growth soon, or the NBA might give up on him. Luckily for Carter, at least from a monetary standpoint, the Nets waived him with $3.5 million already guaranteed for the '22-'23 season, so any new contract is just additional earnings.
 
Cap Considerations
Carter will be an unrestricted free agent with a $1.8 million cap hold and Non-Bird Rights. This means that the highest starting salary the Bucks could offer him using the Non-Bird Exception is $2.3 million. Alternatively, the Bucks could use their their Mid-Level Exception to re-sign Carter if he demands more than $2.3 million. 

Other teams will have multiple ways to sign Carter as even teams without cap space could possibly use any of the Non-Taxpayer MLE, Taxpayer MLE,  or possibly even the Room MLE or Bi-Annual Exception to sign him. It's also possible that Carter only gets minimum offers.