Strangely 4K monitor will only run at 30hz (used to do 60hz) when another monitor is plugged into the PC's HDMI port - USBC-6950-HDMI - Plugable Support
ViewSonic VX2880ml 28-inch 4K 30Hz Monitor Review
ViewSonic VX2880ml 28-inch 4K 30Hz Monitor Review
Microsoft slashes price of Dell 4K 30Hz monitor to $300 in Cyber Monday Extravaganza | TechSpot
Kvm Switch 2 Monitore, Steetek 4K@30Hz USB2.0 HDMI KVM Switch Dual Monitor, HDCP1.2 2 PC 2 Monitor Switch mit Hotkey und Button Control für Tastatur, Maus, Drucker und HD-Monitor : Amazon.de: Computer
2 Port Usb Hdmi Kvm Switch, 2 Pc Yeemie 1 Monitor 4k @ 30hz Hdmi Kvm Switch für 2 Computer Teilen Tastatur und Maus, 3 Usb2.0 mit 2 HDMI zu USB HDMI | Fruugo DE
Stuck on 4k @ 30hz? How to get 4k @ 60hz on your PC - YouTube
StarTech.com USB32HD2 | StarTech.com USB 3.0 to Dual HDMI Adapter - 4K 30Hz - External Video & Graphics Card - Dual Monitor Display Adapter - Supports Windows (USB32HD2)