Trouble is, on this new monitor, which has a controller type joystick control for the on-screen menu, you have tap right-right-right-down to switch inputs. Not really an inconvenience - I'm used to it. But I'm very concerned that I will wear the control out eventually since I switch back and forth a lot.
So I decided to buy a DP KVM. Trouble is, most of them only support 100Hz at 2K and 4K.
I did a lot of research and found out that, despite being a digital signal, DP is very fussy about cable length - especially when used on a KVM. 10 feet is the max you're ever supposed to run DP 1.4. Dell and other manufacturers recommend 6 feet.
Cable standards are also very loose. You need a DP 1.4 cable for my monitor (DP 1.4 are also called 8K cables because they are the minimum to support 8K at 60Hz). I've never seen DP 1.4 printed on a cable, though, and there is no official DP 1.4 marking, although it is generally accepted that a connector with 8K printed on it is DP 1.4.
I read a lot of KVM reviews and Reddit forums and most issues were related to the cables. All KVM manufacturers recommend no longer than a 5 foot cable on any of the KVM inputs or outputs, but cable quality varies.
I finally settled on this KVM, which is $190 (yeah, DP KVMs are pricey):
https://www.amazon.com/dp/B0BRHXT5WG
It's rated for 144Hz at 2 and 4K, it had excellent reviews, the build quality is solid, it's a metal case (hey, good shielding right?) and (a rarity) it comes with it's own DP cables that are 5 feet long, and have toroidal chokes in the cable to block radio noise from the PCs. The manufacturer only guarantees the KVM to work with their cables.
Sadly, it did not work for me. It worked rock solid at 100 Hz, but like one other reviewer, I got screen glitches at 144Hz (and even 120) no matter what I tried, which included swapping out the monitor cable for a short high quality 1.6 foot DP 1.4 cable. Maybe my monitor is just picky. Sadly, I returned it. I can recommend this unit if you only need 100Hz, and the price is actually pretty good if you consider that it comes with all the cables, it even has USB audio built in, and a USB 3.0 hub. It even supports a hotkey on the keyboard to switch monitors.
I read a lot more recommendations on Reddit, and found a lot of people had better luck with just a much simpler DP 1.4 A-B switch. I would need to continue using my old VGA KVM for the mouse and keyboard, but that's fine. I found this one for only $23 (with no cables) that supports up to 240Hz at 2 and 4K:
https://www.amazon.com/dp/B0BQBKK1K5
It's not shown in the photo, but the switch has a USB-C connector for power.
I also bought two 5 foot DP 1.4 cables from a highly recommended manufacturer, and I also have their 1.6 ft cable which I used between the switch and the monitor:
https://www.amazon.com/dp/B09TVV4B9M
This works like a charm, so far. I played several hours last night, on a variety of games, and no glitching.
I tried a 6 foot cable and immediately got glitching on the gaming PC, but the 5 foot cable does, just barely, reach. I did need to use the 6 foot cable on the workstation to avoid moving it, but I'm running that at 100Hz and it works fine.
Very tedious experiment, but it's up and working, and now I'm not worried about wearing out the monitor controls.
Another consideration if you use a gaming mouse or keyboard with a KVM, is you want to try to keep the mouse and keyboard refresh below 750Hz, if it's adjustable. Most modern KVMs will handle that just fine, and that's plenty for gaming (standard non-gaming mice are usually 120 or 240Hz).
Also, some KVMs have a special mode or port for RGB keyboards. My Corsair keyboard's RGB would not work with that fancy KVM I first tried, until I moved it to the USB 3.0 hub on the KVM, which the manual recommended (my keyboard and mouse work fine on the old VGA KVM).
I wound up tie-wrapping the switch to the monitor pedestal. The small button on the desk underneath is the remote button for the VGA KVM I use to switch the keyboard and mousez:
