When used inside a Unity Package, TypeOptions(ShowAllTypes = true) will not show Types from the main project

[maziluradu]

When used inside a Unity Package, TypeOptions(ShowAllTypes = true), will only show Types which are part of the assembly of that Unity Package, and not Types from the "main" project.

A workaround is using:
[Inherits(typeof(MonoBehaviour), IncludeAdditionalAssemblies = new[] { "Assembly-CSharp" })]

However, by using this workaround, Types defined in a separate assembly inside the "main" project will still not show - a package will need to specifically include the separate assembly name from the consuming project inside the "IncludeAdditionalAssemblies" array.