There actually were Nubian pharaohs for a period (the 25th dynasty, to be exact).
I don't think they are doing it for that reason, let's face it. They are representing North Africa's history. So they choose to select the New Kingdom's one foreign black dynasty from Nubia, to represent the history of a region of Africa who's native people predominantly look caucasian like the photos above? We know why. They made his features appear, if anything, African American, who are part European part West African in phenotype:
West Africa lies at the other side of of a 5000 mile continent. Also the other side of the Sahara.
There are very few routes across the Sahara. Also Afroasiatic languages like Egyptian likely originated in Asia.
Likely the Afroasiatic family of languages like Egyptian, Hebrew, Arabic, originated in the Natufian culture of the Near East.
Even if we charitably say he is meant to be from the Nubian 25th Dynasty that ruled Egypt, or he is mixed race, such as a Egyptian-Nubian prince, the nearby Nubians don't look very much like a typical African American actor or model from Hollywood. Even further south on the Nile, the Nilotic peoples don't look like West Africans either, having tall gracile features. His appearace is more likely inspired by 1960s African American 'black power' views of Egypt, where Egyptian and Nubian culture were appropriated to give African Americans a claim to a civilization as old as China or Greece. The subculture of African American known as 'hoteps', known more recently known as 'kangz', who's ancestors came from nowhere within 4000 miles of Egypt.
Total War is likely virtue signalling to pan-Africanist 'black power' myths from the USA. To appease activists or prevent bad press.
A while back, they did genetic studies on 151 ancient Egyptian mummies, from from Abusir el-Meleq in Middle Egypt. They found that the population was slightly mixed, as we would expect, but this had actually increased since ancient times, meaning Egyptians are 'blacker' today than they were in ancient times (likely due to the medieval Arab slave trade poaching sub-Saharan Africans for export in the Muslim world):
The absolute estimates of sub-Saharan African ancestry in these three ancient Egyptian individuals ranged from 6 to 15%, and the absolute estimates of sub-Saharan African ancestry in the 135 modern Egyptian samples ranged from 14 to 21%, which show an 8% increase in African component. The age of the ancient Egyptian samples suggests that this 8% increase in African component occurred predominantly within the last 2000 years.
Furthermore, concerning modern Egyptians:
A study by Luis et al. (2004) found that the male haplogroups in a sample of 147 Egyptians were E1b1b (36.1%, predominantly E-M78), J (32.0%), G (8.8%), T (8.2%), and R (7.5%). The study found that "Egypt's NRY frequency distributions appear to be much more similar to those of the Middle East than to any sub-Saharan African population, suggesting a much larger Eurasian genetic component ... The cumulative frequency of typical sub-Saharan lineages (A, B, E1b1a) is 3.4% in Egypt
Furthermore, concerning Copts in Sudan:
45% of Copts in Sudan (of a sample of 33) carry haplogroup J1. Next most common was E1b1b, the most common haplogroup in North Africa. Both paternal lineages are common among other regional Afroasiatic-speaking populations, such as Beja, Ethiopians, and Sudanese Arabs, as well as non-Afroasiatic-speaking Nubians. E1b1b reaches its highest frequencies among North African and Horn of Africa populations such as Amazighs and Somalis. The next most common haplogroups borne by Copts are R1b (15%), most common in Europe, and the widespread African haplogroup B (15%)
The native people of the region seem to share the E1b1b haplogroup with Jews and Europeans (Hitler was E1b1b, as are many modern Europeans, but it was probably from ancient Asia or North Africa in origin). Even more lol, Tutankahmun had R1b hapogroup, which is, of course, famously associated with Aryans. That must have been a major blow to hoteps. The other big hapologroup was J, found mostly in Arab peoples.