This post shows you how to fix "asp-controller and asp-action attributes not working" or "form asp-action in areas. Can't find a controller. Asp.Net Core".
In your areas create a _ViewImports.cshtml file, then copy the one from your main ~/Views folder.
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
I think the problem is VS Intellisense doesn't load your tag helpers for your areas.