I've installed Ubuntu 19.10 from the default image for Raspberry Pi 4B. I've tried two screens, but the screen resolution(s) are not detected. Only one resolution is offered. For example, on the smaller screen, which is 1280x800, the only resolution offered is 640x480.
However, on my laptop (also on Ubuntu 19.10) both screens work fine (offering a range of resolutions are you would expect).
What do I need to do on the Raspberry Pi to get this sorted out?