Summary
After missing only 33 games from 2012-2020, Harden has missed more than that in the last two seasons. There's chance that Harden won't be as durable going forward as he ages into his mid-thirties, and his hamstring has continued to bother him throughout the '21-'22 season. Other than brief stints of great play, Harden just hasn't looked like himself, particularly driving to the rim, and that's backed up by the numbers as he is shooting below-average at the rim for the first time since his rookie season. 

Not long ago, Harden was an MVP-level player, and one of the greatest scorers of all time. He could hit contested step-back threes, had a dangerous floater game, and had the craft to finish effectively at the rim. Despite not looking like the most athletic guy, he could blow-by defenders with his change of pace and ball-handling skills.

Unfortunately, his struggles to finish at the rim have hindered all of those aspects to his scoring game. With his driving ability not being as much of a threat, defenders can press up on him more, making his step-back game less potent. 

Harden was one of the best passers in the league, and that skill may be the one thing that stays as he ages. Harden can carve up defenses in pick-and-roll through slick pocket passes to the roller, accurate lobs on alley-oops, and lasers to weakside shooters.

Defensively, Harden has always been a minus but can survive as a decent on-ball defender and stout post defender. It's off-ball where he has most of his struggles, either losing his man or failing to rotate to help. Harden's limitations on defense make it so you almost have to switch a lot as a team.

Harden is at the age where it might be smart to lock down as much future money as possible, but I also wouldn't blame him for taking shorter-term deals in order to give himself more flexibility, or to try and improve his stock heading into a different summer, especially considering how much money he has already made.
 
Cap Considerations
Harden has a $47.4 million player option for '22-'23. If he opts out, Harden will be an unrestricted free agent with a $46.5 million cap hold and full Bird rights. Since Harden will have a large cap hold, the 76ers will not have any cap space unless Hardens opts out and leaves in free agency, so his cap hold isn't really relevant. 

If Harden becomes a free agent, the 76ers can offer him up to a 5-year, $270 million max contract. He could opt in and later agree to an extension. Such an extension would include four years and $223 million on top of his current contract.

Other teams will be able to offer Harden a 4-year, $200 million max offer, with a player option and 15% trade bonus as possible sweeteners as well. Harden could also sign a shorter-term contract if he wants more flexibility. Since few teams have cap space, any team looking to acquire Harden would likely do so via sign-and-trade or trading for him after he opts in.