If one opens Documentation from the Help menu, it becomes a window one can access via a command key (e.g. Cmd-2 or Cmd-3, etc.). Since it is always the same content (that is, Documentation), it might be better if it had a contact keyboard shortcut. Since Cmd-0 (zero) does not seem to be in use, how about that?
You can add a shortcut to open documentation in the Xojo Preferences → Edit Shortcuts.
However, using the Command Key to open the Documentation also causes the documentation window to reset to its tiny default size.
Opening documentation with the menu also opens it up tiny, with no way to move it around, resize or even close.