Hi Jeff - welcome to the forum!
There are various ways of using a bigger monitor to display the ARC screen in portrait mode, depending on what device you are using. If you do an internet search, you will get a few discussions looking at this with ARC, but there is more info for other applications, including shop store displays. However, it’s not always straightforward!
The easiest method I’ve seen is to use a digital projector via an HDMI adapter and cable. You get a perfect portrait display of the ARC screen and as big as you want it...
Another option is to try the Magic app for Scalextric ARC, which has a landscape display as default. https://www.magicstudio.eu/index.php/games/arcapp