Summary
After early success in Phoenix and Washington, Morris seemed to have fallen off around 2019, being bought out twice in a two year span - once by the Pelicans after being traded from Washington, and once by the Pistons.

However, after joining the Lakers mid-way through the '19-'20 season, Morris briefly revived his career as a rotation player for a championship level team. However, Morris struggled in his second season in Los Angeles in '20-'21, struggling to hit shots from outside by only hitting 31% of his threes. Morris then missed the majority of the '21-'22 season due to injury, and was never able to make an impact with the Heat. In the last two seasons, he didn't play enough minutes for the Nets or Mavericks to prove he can still contribute.

Morris is not a great defender, but he's big enough to hold his own against some of the bigger wings in the NBA. The Lakers even used him as a backup center in certain units. His versatility to play either big position gives him some intrigue for teams needing a small-ball big option.

If Morris can get healthy and hit enough outside shots, he could become a solid rotation-level player again. The Nets signed him in hopes he could give them another option as a small-ball center, and if he can fill that role adequately, either for the Mavericks or elsewhere, he could revive his career. Otherwise, he may be outside of the NBA soon.
 
Cap Considerations
Morris will be an unrestricted free agent with a $2.1 million cap hold and Early Bird rights. Since the Mavericks will be operating over the salary cap, they will retain Morris' Early Bird rights until he is re-signed or signs elsewhere. The Mavericks could offer Morris a starting salary of up to 5% more than the average salary (likely around $13 million) using the Early Bird exception, which should be enough should they wish to bring him back.

Other teams will have multiple ways to sign Morris as even teams without cap space could use any of the Non-Taxpayer MLE, Room MLE, Taxpayer MLE, or Bi-Annual Exception to sign him. It's also likely that Morris only gets minimum offers, and may not even get fully-guaranteed offers.