Summary
While Muscala has consistently shot well from outside, he isn't an elite outside shooter, and doesn't really do anything else. He shot 43% from three in '21-'22, but for his career has hovered around the high-30's. Stretch bigs can be valuable, and Muscala has had some nice moments for the Thunder in recent seasons, so teams would likely have some interest if he hits free agency in 2022.

Defensively, it's unlikely that Muscala can provide the level of rim protection necessary to anchor a defense, and he doesn't move all that well laterally on the perimeter either. However, the Thunder have actually had an above-average defense with Muscala on the court over the last few seasons, although there is likely some noise in that data and is unlikely to be due to anything Muscala is specifically doing.

I was surprised that Muscala got more than the minimum in 2021, but I think part of that was more of a favor to Muscala and to give the Thunder more salary to potentially use in a trade (although he did have an implicit no trade clause for the '21-'22 season). Since his option isn't for that much more than the minimum, and since the Thunder seem to like Muscala and may be operating over the cap anyway and not need the space, they will likely exercise the option to keep Muscala in '22-'23.
 
Cap Considerations
Muscala has a $3.5 million team option for 2022-2023, and if that is declined he will be an unrestricted free agent with a $6.7 million cap hold and Full Bird rights, meaning the Thunder would have no restrictions on re-signing him.

If he becomes a free agent, other teams will have multiple ways to sign Muscala 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 Muscala could be had for the minimum.