That's not saying the king was black. Even in the link you posted you can click moor in the tag and see the same style used multiple times.
armorial.library.utoronto.ca
Here in this wiki link you can see the same.
en.m.wikipedia.org
en.m.wikipedia.org
Why would the black royalty allow their portraits to be painted as white people (some of which show black people in servitude) and all agree to use the same generic head of a black person for the royal crests?
I've seen every video you posted multiple times and read everything link you sent and no claims have solid sources in fact I find way more evidence that supports the opposite of what you claim.
Even something like the Stuart - Svart connection I can't find anywhere other than a Pinterest post that links to this:
No etymological source to back the claim other than the words look similar but you can find plenty of information showing Stuart - Steward - Stewart connection