OMG if it's anything like the process and stability with the Galaxy Watch 3, they can keep it. Just stick with a Standard old fashion sim card. My watch has been the most unreliable device I've ever owned and it's just gathering dust. Sammy has to work on this as it's horrible.
I thought I read the S21 (and S20) both have eSIM capability. I can't remember if what I read stated it would be available in the US (I thought it did).