Summary
Prior to joining the Bucks, Portis was known as a one-dimensional, inefficient scorer. In '19-'20 with the Knicks, Portis had a 50.3% eFG%, which was in the 18th percentile for his position, per Cleaning the Glass.

However, Portis lit it up in '20-'21 in the Bucks spacing, shooting 47% from three. While that level of shooting was never going to continue, he still shot 40% from outside in '21-'22. However, due to him not being the most athletic guy, he struggles to finish inside, as his field goal percentage at the rim has consistently been poor for a big. 

While playing Portis at the five can create a lot of spacing and shot-making on offense, it can really hurt your defense. Portis was never a strong defender as a power forward, and at center those deficiencies became even greater, as having no rim protection can be a death sentence for a team's defense. In that regard, Portis benefits greatly from getting to play next to Giannis Antetokounmpo, but other teams need to consider that when they think about his fit with a different roster.

After not seeing a ton of minutes in some early playoff games in 2021, Portis was big for the Bucks in the later rounds of their championship run, using his size to bully smaller players inside and on the offensive glass. With P.J. Tucker leaving in free agency and Brook Lopez missing most of the season, more has been asked of Portis on both sides of the court, and he played well, but didn't have the same level of playoff success that he did in 2021.
 
Cap Considerations
Portis has a $4.6 million player option for 2022-2023, and if he opts out he will be an unrestricted free agent with a $5.7 million cap hold and Early Bird rights. Since the Bucks will most likely be operating over the salary cap, they will retain Portis's Early Bird rights until he is re-signed or signs elsewhere. The Bucks could offer Portis a starting salary of up to 5% more than the average salary (likely around $10.9 million) using the Early Bird exception, which should be enough to retain him.
 
If Portis demands a starting salary of more than the full $10.3 million Non-Taxpayer Mid-Level Exception, only teams with cap space will be able to sign him, unless a sign-and-trade is worked out (although his starting salary in a sign-and-trade would also be limited to not much more than the full MLE, due to the Bucks having his Early Bird Rights, as stated above). It's likely that Portis could be had for the full MLE or slightly less, including possibly the Taxpayer MLE.