UPERFECT Portable Monitor 15.6 inch, 1080P FHD USB-C Portable Laptop Monitor HDMI Travel Monitor w/VESA & Smart Case, Matte IPS Display Eye Care External Screen for Switch/PS5/PC/Phone

I’ve had the older model 15” Uperfect 1080p that I used as a second monitor and as a Steam Deck monitor. Worked great for both. You’ll need a steam dock or USB hub to charge the Steam Deck and power the monitor unless you want to drain your battery (the monitor does work directly from the steam deck if you need to for short periods of gaming)