@sdetweil In case for some reason it’s helpful, I’ve reviewed the contents of /boot/config.txt from my two devices (4B gets errors, 2B does not).
In 2B, not in 4B:
#dtoverlay=vc4-kms-v3d
# see https://forums.raspberrypi.com/viewtopic.php?p=1507622#p1507247
dtoverlay=vc4-fkms-v3d
In 4B, not in 2B:
dtoverlay=vc4-kms-v3d
# Run in 64-bit mode
arm_64bit=1
[cm5]
dtoverlay=dwc2,dr_mode=host