Hi Guys/Girls,
I have also the same phenomenon. After a successful upgrade from Mojave to Catalina 10.15.7 (following the install/upgrade guided after a hang installed the SSDT-EC.aml), the upgrade had some headaches but almost everything works. But since the upgrade my secondary monitor does not work anymore, its on HDMI and when plugged in while booting the system hangs at:
: IOConsoleUsers: gIOScreenLockState 3, hs 0, bs 0, now 0, sm 0x0
When I remove the HDMI cable it boots like a charm.
Running on a HP Pavilion AIO with i5 Haswell and according to the specs, my graphic card should be a Intel® HD Graphics 4200. (But also saw 4200?)
Perhaps there is already an issue posted with my specs?