Big monitor stays black after using built-in KVM switch

I'm using a Philips Evnia 49M2C8900 32:9 screen. It is running at 5120×1440 pixels @ 240 Hz. My main computer is attached to DisplayPort. It has an Nvidia RTX4080 installed and is running Ubuntu. Everything was fine with Ubuntu 24.04 but since I upgraded to 26.04 I can't really use the built-in KVM switch of the screen anymore. When I switch to another input and back to DisplayPort the screen just…