Why am I not able to replace to Android 11?

I’ve been checking for instrument replace on my Galaxy S10+, the prevailing model is Android 10 and One UI 2.1, I imagine there must had been an replace to be had to Android 11 and One UI 3.(*3*), but it surely assists in keeping pronouncing it’s up-to-the-minute. (*2*)My Galaxy S10+ is america model, SM-G975U, even supposing I take advantage of it in Nigeria.(*1*)