See here, it's a technical limitation of the display:
Your options are to decrease the font DPI so items on the screen are smaller, as the resolution cannot be changed.
For Welcome in particular, I'll note down that the window should not have a minimum height/width, and may require some optimisations for small displays. We could add support for this display and maximise it by default.
Another option is to force Welcome to use smaller text. You can run this from the terminal (or edit the launchers in the main menu)
ubuntu-mate-welcome --font-dpi=51
(DPI must be between 50 and 250, 96 the is default)