I do think he would welcome them with open arms. In fact I have very little doubt about that. His laserlike focus on the southern border as a source of terrorism threats and illegal narcotics while completely ignoring the northern border which is actually
the more dangerous one for terrorist passage and the source of
the most dangerous opioids entering the country from abroad is just one of countless examples of him making decisions based on the skin color of foreigners rather than objective facts.
But the question also implies a limited view of racism, and ignores my basic point. Even if he didn't, that would be discrimination based on national origin, obviously. Countries don't emigrate, people do. And there is no rational reason to discriminate against the entire continent of Africa- as I said even if you think it's poor or uneducated or whatever on average that's obviously not true everywhere, and I'd argue that believing it to be is very clearly racism given that the only commonality that covers basically the entire continent is darker skin color. So why group it together? It might be racism borne of absurd ignorance rather than malice, but that doesn't make it not racism.
As I quoted a couple days ago, "racism is not merely a simplistic hatred. It is, more often, broad sympathy toward some and broader skepticism toward others." Trump is clearly guilty of broad sympathy towards white people and broader skepticism towards non-whites, both in the "####hole countries" rant and in many, many other examples.
FWIW I do agree with your point about MAGA hats and Trump supporters, though. It's unfair to call them racist based on solely the hat or their support for Trump. I've been railing against that since before the election and will keep doing it. They are people who accept Trump's rampant bigotry and misogyny and don't think those things should disqualify someone from the presidency. That is damning enough, no need to imply something that isn't there.