If it doesn't need to be held in your hand, a VR headset makes for a pretty good incredibly low-latency portable monitor. It can even be 20 foot tall and through the wall if you want it to be. And with a VR headset, you can just use whatever controller you already normally use for your PC. Plus, since you can put the virtual monitor anywhere, you can relieve all the pent up neck strain from playing phone games by putting the screen at a comfortable height, and even move it further up when you want to recline in your chair.

I recommend the virtual desktop software, but there are plenty of options. A modern VR headset like Quest 3 or Pico 4 can make the equivalent of about a 1440p 120hz monitor at a comfortable field of view. Though using those settings does currently require that your real monitor be capable of them. But a 1080p 60hz monitor is good enough for most stuff anyway, and that's much more accessible. Then you could even go as cheap as a Quest 2. But honestly, I recommend the 3 at this point anyway. It's a huge jump over the 2.