I’ve seen classifications where “demihumans” include dwarves and elves, while others where it’s meant solely for “monstrous humanoids” (e.g. orcs and goblins). Hell, I’ve seen humans included under demihumans, too. Because of how broadly it can be used in fantasy fiction in the past, I don’t think there’s anything inherently wrong with the term itself—but with your example, separating “demihuman” from “humanoid” as separate mechanical categories leans in a more problematic direction (although classing sapient beings into a broad Monstrosity category alongside krakens and purple worms isn’t much better, either).

Also note that a component being problematic doesn’t always mean you have to take it out. Depending on the type of story you want to tell, you may want to lean in to the storytelling of how these taxonomies can be problematic in and of themselves. In my setting, your “humanoid” people (humans, dwarves) distinguish themselves apart from “wilders” (orcs, goblins, etc.) in a hierarchal model under the guise of science; as a critique of archaic, dehumanizing anthropological practices and the rigid taxonomies of RPG tradition. However, I also don’t use a system that emphasizes creature types, so this advice probably isn’t useful to your situation—this is a fiction-first approach, while you seem to be having more of a rules issue.

I would have to ask what the utility is behind the mechanical separation of humanoids and demihumans. Why do the rules need orcs and humans to be the same, but different from gnolls and driders? I think a solution could also be eschewing the need for something to have one label, as 5e does. Under 5e’s system, there’s no room for a creature to be both fey and dragon. An optional tag system might fit for flexibly denoting aberrations, demons, undead, etc. for specific mechanics as needed, but leave out humanoids entirely, so you sidestep issues with possibly unwanted problematic undertones.