No video, but I wrote up a guide for this as well to more simply focus on this “Firmware Update” need when OTA (and adb) updates are broken.
I am guessing it displays something to the effect of “Orange Mode: OS is not verified or custom OS” which is their wordy way of saying the device is unlocked. Note that just selecting “Allow OEM unlocking” in Developer options in the OS should not give this message, you would have to have unlocked it from the bootloader with a fastboot flashing unlock. Did you do this, or has this message been flashing by since you first got the device?