The two fixes are the most common. I generally use the UPN user@internal.domain.tld. You'll also need to be sure that your internal AD DNS is configured on the vnet DNS configuration.
A good way to test is to create a general stand alone windows VM in the same resource group and use the same subnet, then try to join it to your AD domain, if it works, you know you made a mistake in your WVD VM configuration. If not, it is probably one of the 2 fixes in your post.