I attempted to perform an erase and install on a 2018 MBP after installing Catalina. I booted to internet recovery so I could downgrade to Mojave. When booting into internet recovery it comes up with a screen that say "Activate Mac" and message at bottom "The certificate for this server is invalid. You might be connecting to a server that is pretending to be "tbsc.apple.com" which could put your confidential information at risk". I only have the option at the bottom of the screen to restart. If I browse the options on the menu bar at the top I see the option to deactivate and erase but this just spins and restarts the machine.
The machine does not allow me to boot into target mode, reset NVRAM, or even option boot. All boot attempts go straight to internet recovery and back into the loop.