Change max resolution of Pi 4:
------------------------------
In the "/media/puffin/system-boot/config.txt" file, add this line:

hdmi_mode=16

This will max out the Pi 4 to Full HD 60fps.
------------------------------------------------------------
Source:
https://pimylifeup.com/raspberry-pi-screen-resolution/

Date: January 26th, 2021

Update: July 16th 2024:
You may want to try
hdmi_mode=4
for a 720p 60fps mode (for software acceleration OS's like Windows 10).