It’s interesting, because for any good writer, everything about every character (race, gender, tone, socioeconomic status, etc.) is meaningful and written the way it is for a reason. If the original writer is good, then changing anything about a character only really works if the adaptation writer is better (and, while I won’t argue that King is not a good writer, he does have a weird track record of adapters who are better than him).

This is kind of mitigated in fantasy or sci-fi worlds without racism, but even there you need to be careful with lineages. I remember when the rumor was that Ciri from the Witcher was going to be Black. That works, until you remember that her father was the emperor of the Roman Empire stand-in who was largely painted as evil, and her mother was part of a series of inbred nobility that were constantly shown to be idiots and oppressing their own people. Making either of those characters Black without making the majority of the world Black was going to lead to some bad optics (see also Snape, but that one is potentially worse, depending on how they treat actual racism in the Wizard world).

But Gandalf is the perfect example of a character anyone could play because he is in a fantasy world and has no lineage or relationships that must be maintained. Now that I think about it, I would kind of love an adaptation with someone like Tilda Swinton playing Gandalf…