TextBox1 = "Text"
This was really shorthand for ...
TextBox1.Text = "Text"
... because the Text property was the default property.
VB.NET continues to include a "Default" property attribute, but it's not at all the same. In fact, the way it's really used is documented in such an obscure way at Microsoft that there is a real need for some clarification.
The Microsoft documentation for declaring a Default Property in a Class definition is fairly straightforward. But you have to read the whole thing. The initial step-by-step instructions don't work. You could get the idea that all you have to do is simply use the Default keyword instead of Private, Public, or Shared.