I’ve found the following works. There may be ‘better’ methods in the RPi forums.
Boot with your display attached and make sure you can get all the display modes you expect.
sudo mkdir -p /lib/firmware/edid
sudo cp /sys/devices/platform/gpu/drm/card0/card0-HDMI-A-1/edid /lib/firmware/edid/edid.dat
Then edit /boot/cmdline.txt (sudo nano /boot/cmdline.txt)
root=/dev/mmcblk0p2 rootfstype=ext4 rootwait quiet osmcdev=rbp2 drm.edid_firmware=HDMI-A-1:edid/edid.dat video=HDMI-A-1:D
Note that tvservice no longer works as it used to.
I don’t think anything special is needed in config.txt with the recipe above.