I really don’t get the upset about a fictional people from 20,000 years in the fictional future not being represented by an ethnicity of today.
However, let’s say for a minute that these are future Muslim/Arab/Bedouin people of some sort(even though that goes against cannon). I wouldn’t call the Fremen in Dune a positive representation. They are a powder keg of intolerance and violence, with mild cannaibistic tendencies, that quickly explode into genocidal intergalactic genocide. The protagonist actually compares himself and his followers to Hitler and the Nazi SS in the second book.
To me this looks like a no win situation. Make them ethnically indistinct and you are white washing, or not giving representation. Do it, and follow the cannon material, and you are going to get hit with Islamophobia claims.