The biggest mistake is that BBCodeView is not anchored to all sides. A layout without anchors is a broken layout.
The second mistake is that you are creating a light theme but the main app theme is still set to a dark theme.
Change in the manifest editor:
CreateResourceFromFile(Macro, Themes.LightTheme)
The last mistake is that you are not setting the view size:
BBCodeView1.Text = _
$"[Color=#ff0000]Hello world!
Please enter your number (1 - 100): [vertical=10][view=txtInput Width=80 Height=50/][/vertical]
[b]Hello[/b] [url]world![/url][/color]"$