Bottomline, if you're getting error 9000f, the only way ressurect a bricked MacBook Pro with a T2 security chip is to re-install MacOS Catalina Beta.
Then I tried using just Cmd ⌘ + R combination while booting up and somehow this time I was able to get to the installation screen that only allowed me to install Catalina Beta (which is okay instead of having a bricked laptop and a possible trip to the Apple store).I also tried using Cmd + Option + R to boot into recovery but got the same error again.With a freshly wiped SSD and no option to boot using any external drives, I decided to go with internet recovery by pressing Cmd + Shift + R which then asked me to connect to a WiFi, downloaded some stuff with the spinning globe on the screen, then straight away gave me the 9000f error.How I was able to get rid of error 9000f?
I didn't know that with T2 security chips, you have to enable external drive boot or else you almost brick your laptop. The system offered to 'Starting Internet Recovery' from the WIFI. Next restarted Mac to boot from the flash. I did not read any downgrade procedure and just booted into recovery and used disk utilities to wipe the SSD. Enter to recovery mode and erase main disk. I installed MacOS Caltalina on my 2018 MacBook Pro with T2 security chip, used it for about 2 weeks and then decided to go back to Mojave because some of the programs that I use for Web development and photo editing stoppped working correctly. I got this error 9000f yesterday and fortunately I was able to fix it by booting into recovery mode using Cmd ⌘ + R and re-installing MacOS Catalina Beta.