If I try to create a mii from an amiibo on my Nintedo Switch, it will say that a mii is not registered to it

My amiibos were registered using my Wii U. This occurs even if I use a different controller, use a different amiibo, or register the amiibo again using the Wii U.

You probably haven't saved any new data to your amiibo for a while and there seems to be a new data format for amiibos. You have to resave your owner information on your amiibo on an updated device. It appears the format for the owner information has changed at some point and the Switch is expecting the newer format. I can verify this works for the New 3DS, but I suspect (hope) it will work the same on the Wii U.

Open the amiibo Settings in the home menu settings and look at the current registration for the amiibo you're trying to use. For the owner mii, choose Change and choose your Mii again (you must do this, otherwise saving does nothing). Then save the info back to your amiibo. It should work then.