Summary
Despite reviving his career in Golden State, many people (including myself) doubted that he could contribute to the Lakers. It was one thing to catch lobs playing with the most talented team ever assembled and protect the rim when you have an elite defender in Draymond Green next to you and additional size at the wing with Kevin Durant, but I didn't think he could contribute in a non-perfect scenario.

However, McGee certainly contributed for the Lakers, starting the entire regular season in '19-'20. His minutes fell drastically in the playoffs, as he was taken out of the starting lineup and sometimes didn't even get minutes. McGee has always been a good finisher at the rim due to his size and athleticism. He has a big catch radius and good hands, allowing him to catch tough lobs and finish in traffic. On defense, he chases blocks a little too much, but can be a legitimate deterrent at the rim.

McGee struggled this year with the Cavaliers and Nuggets, as his 66% shooting at the rim is his worst in a decade, according to Cleaning the Glass. Some of that is likely due to situation, as McGee tends to get a little careless when he's not on a title contender, but didn't give the Nuggets much help in the playoffs either. There's a chance though that some of that might be due to age-related regression, which teams will certainly want to monitor before signing McGee this summer. McGee will be 33 years old as a free agent this summer, and if he's lost enough athleticism to make him a below-average finisher at the rim, his days in the NBA might be numbered.
 
Cap Considerations
McGee will be an unrestricted free agent with full Bird rights. As his cap hold ($8 million) exceeds the salary he will get in free agency, his cap hold is not really relevant, as the Nuggets will be operating over the cap this summer.

Other teams will have multiple ways to sign McGee as even teams without cap space could possibly use either of the Non-Taxpayer MLE, Taxpayer MLE, or possibly even the Room MLE to sign him. It's also possible McGee only gets minimum offers this summer.