Summary
After shooting 39% from three each season from 2018 to 2021, Green struggled in '21-'22, only hitting 28% from three. Since one of Green's main contributions is his ability to stretch the floor as a big, that number is concerning. When he was hitting near 40%, Green was a reliable big that could come off the bench but still potentially close games.

Green also took a smaller proportion of his shots from three in '21-'22, and has replaced those with shots at the rim, but he has never been a great finisher inside (his 66% rate at the rim in '21-'22 is decent, but below-average for a big, according to Cleaning the Glass).

Defensively, Green isn't the most mobile player, and has never been much of a rim protector, but he's been able to survive on that end. He's not an obvious target on defense, but he could be if he was surrounded by clearly superior defensive talent, and if he played fewer minutes against second units that don't have the weapons to put as much pressure on him defensively.

Going into the year, I thought Green's player option for '22-'23 was likely going to be right around his market value, but with his shooting slump I think he is more likely to opt in. The Nuggets would have little means of replacing him if he opted out given their cap situation, so he could use that as leverage. However, the Nuggets may be okay with him leaving considering re-signing him could cost them a lot in luxury tax penalties, especially since he shot so poorly in '21-'22.
 
Cap Considerations
Green has an $8.2 million player option for 2022-2023, and if he declines that option he will be an unrestricted free agent with an $10.7 million cap hold and Early Bird rights. Since the Nuggets will be operating over the salary cap, they will retain Green's Early Bird rights until he is re-signed or signs elsewhere. The Nuggets could offer Green a starting salary of up to $14.35 million using the Early Bird exception, which should be more than enough should they wish to bring him back. 

For other teams, if Green 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 completed), but it's possible that Green could be had for the full MLE or less.