Is the Pi3 running the same version of LE as the Pi4?
It is more likely a change in behaviour due to different versions.
All the "hdmi_" settings you've mentioned apply to the deprecated firmware display driver.
LE10/11/12 use the kms driver (kernel side) rather than fkms (firmware side) used by LE9.
The kms driver does rely on a fully working hdmi cable (i.e. reporting hotplug and edid correctly).
The fkms driver was more likely to somewhat work with a faulty cable.
As a simple test, connect the Pi4 to the display without an sdcard inserted.
It should show a diagnostic screen, that includes info about hotplug (HPD) and edid.
What does it show?