This article hit on Garza's NBA prospects pretty well. They have several quotes from NBA execs about him.
The short summary is: Garza is not someone you're going to spend a high draft pick/lots of money on at the NBA level. However, he's so good at the college level that *someone* has to take a flyer on him and see if he can make it. They acknowledge he's not even close to athletic enough to keep up with NBA talent and is ah huge defensive liability. The league has moved away from his style (big man post up offense), but that doesn't mean he can't carve out a niche bench role and bring in a few mil a year for several years. IF he can translate his game into that type of role, the execs say he can find a spot in the right team. Though, the odds say he ends up making a nice career over seas.
https://www.si.com/college/2021/03/22/luka-garza-nba-future-iowa-march-madness-daily-cover