Upgrading a popular line of products may sound like a good idea, but adding larger / better / faster parts to an existing product can create unforeseen problems. For example, putting a more powerful motor in an existing vehicle platform seems to work at first until people report that the increased torque is bending the frame. In the Raspberry Pi world, it seems that the "updated engine" in the Pi 4 causes the WiFi to stop working under certain circumstances.
[Mike Walters] checked for a radio frequency problem on a Twitter post on this issue with a HackRF. It turns out that at this screen resolution, the Pi 4 emits RF noise that is exactly in the range of WiFi channel 1. It appears that the Pi 4 is acting as a wifi jammer for itself.
This story is pretty new so hopefully the Raspberry Pi Foundation is aware of the problem and is working on a fix. For now, however, it might be best to use a slightly lower resolution if you encounter this problem.