Yes update is not available yet for you. Even though you are on US unlocked model it still depends on what carrier sim you are using and if the update is certified is for that carrier etc. You are using TMobile and the update isn't rolling yet for TMobile or US unlocked model using TMobile sim.
If it's confusing yeah it's little confusing the way Android updates are pushed based on what carrier sim you are using etc. FWIW it's the case even on Pixel phones.
If you want update immediately then if you have a friend on Verizon or Sprint, put their sim on you phone and restart and it'll register that your phone as tied to that carrier and you can pull the update. Once it's updated you can switch back to your TMobile sim. Or you can just wait