Summary
The '20-'21 season was the first season that Thanasis ever got real minutes, and he actually showed some things. He plays hard, defends well, and finishes decently at the rim. However, that's about all he has going for him, as he really just does not have any offensive game.

Antetokounmpo doesn't have any sort of outside shooting ability, and he doesn't make plays for others. He doesn't have the handle to make plays off the dribble, so he's not going to initiate any offense. He's also not as big as Giannis, so he can't quite provide rim protection. If he could do that, he could play more at center which could potentially make him more playable on offense.

Thanasis can provide some minutes on nights during the regular season when you're short-handed, but I wouldn't want him to be anything more than the 11th or 12th man, and Mike Budenholzer did not trust him with any consistent playoff minutes in their championship run in 2021 or in the 2022 playoffs. His regular season minutes also decreased in '21-'22 compared to '20-'21, even with the Bucks suffering from injuries and COVID absences early in the season.

If Thanasis can continue to make improvements and develop his offensive game further, he may be able to get more than a minimum contract. However, as he will be 30 as a free agent in 2022, I'm not sure it's reasonable to expect any significant strides.
 
Cap Considerations
Thanasis has a $1.8 million player option for next season, and if he declines that option he will be an unrestricted free agent with a $1.8 million cap hold. Due to the increase in the salary cap, his minimum salary for '22-'23 is about $50k more than his player option amount, so he should opt out as long as he believes he can get a fully-guaranteed minimum contract. Since they will have his full Bird rights, the Bucks will have no restrictions on re-signing him. 

Other teams will have multiple ways to sign Thanasis as even teams without cap space could possibly use any of the Non-Taxpayer MLE, Taxpayer MLE, Room MLE, or Bi-Annual Exception to sign him. Since he signed a minimum contract in 2021, teams will hope to get him at the minimum in 2022 too.