I have a ring binder book where I print out my session notes, including monster stats. That I have laying flat on the table. For newer systems I also include a cheat sheet for the most important rules (or page numbers in the rule book!). Maps etc. I don't like having a wall between me and my players.

Hi, another comment voting for the laptop (sorry).I have music tabs, plot points and relevant characters notes, and maybe even some images open for locations and scenes. The game I'm currently running comes with a screen (mouse guard) but I've found no good use for it yet, and I roll dice in the open cos not doing so feels silly. But if you really want a screen, most games have some made. Chronicles of Darkness games have tables and how to use xp, but again, never found them too useful. Keeping good flow and an immersive setting for rp is more important to me, and a screen gets in the way.

I actually run without a DM screen. I use my story notes and print up the stats for all enemies that I will run, sometimes I will print out a checklist for plot points and objectives the players hit, and I take notes.

Everything else is in my head.i know the rules back to front, and when I don't, we have a standing table rule to decide on the spot and fix it in the future if the ruling is "wrong," as long as it's not catastrophic.

Our games flow, the story, rp, and encounters are king.

Call Of Cthulhu comes with a DM screen that summarizes the most important rules, at least the edition I had.
As an idea, the things I had to look up most frequently (and under time pressure) were rules on sanity loss, injuries and healing, combat maneuvers, the list of weapons.
I also like to have a long list of NPC names I can just draw from whenever the players decide that a random passerby must be plot-relevant. This can be combined with a list of quirks (limps, shy, drunk, religious, frightened, foreigner, gorgeous,...).
Pick a name, pick 2 quirks, BAM, instant NPC out of the box.

For d&d? https://2014.5e.tools/dmscreen.html on my laptop along with my spreadsheet of notes.

For something less rules-y? Maybe a PDF of the rules, or multiple copies if I need quick reference to several places.

IMHO having a gm screen behind my laptop is more hassle than its worth. So, on my laptop I have internet access and all relevant info in my foundryvtt (all stats of my player characters, the current relevant campaign Info and battle map,...)