Chosen Solution
My MacBook Pro screen is broken and currently using with External Display, I want to upgrade it to macOS Catalina. the problem is I am unable to see what is going in without the laptop screen in order to clean install when I try to boot with Option + CMD + R. I also tried in clamshell mode with Power, External Display and Keyboard connected. nothing shows up. PS: Replacing the screen is not an option for me right now.
Sounds like you’ll need to wait on the OS upgrade until you get your display repaired. Apple requires the internal display to be functional (primary display) in all of their OS installers. Frankly, Catalina is still a bit buggy. I would hold off until the 10.15.1 release shows up.
Unless… if you have friend that has similar mac book pro.. just put your HDD install catalina. Remove that HDD put it on your device.
boot your mac with a systemrescueCD and then use linux command dd to write a complete partition? Or use gparted to copy/clone a working a Catalina from another hard drive inside this?? I have even booted sierra from a external drive! May be OP can try these!!!
Open your mbp, deattach display (use iFixit tutorial), connect your external display and viola. When you finish clean install reattach the display.
