This guide is NOT for any other PDAs, so if you want to apply them at any other PDA other than the Zenfone 6, it might brick your PDA.
Requirements:
A minimum of 8GB is fine, but it's better to have more in this case.
This is the most important step unless the data isn't that important.
The SIM card has to be removed in order to allow you to breeze through any SetupWizard.
If you have powered off your PDA on this step, press Volume up & power button until you boot in fastboot. There, you can either fastboot boot TWRP (if it's somehow not installed), or use the volume buttons to select "recovery", & press the power button to boot there (if TWRP's installed).
Since this PDA force-encrypts by default; it's important to do this step.
At this step, note which slot you're on. By the end of step 8; you're going to be back on that slot.
Vendor can be optionally wiped. However, on the likely event that the device freaks out & shuts off, you'll probably be stuck in fastboot.
This is to upgrade the vendor, and keep TWRP.
This is to ensure latest vendor on both slots. Reboot to recovery after this step, again.
At this point, we're basically done with setting up latest firmware for the 6z, and we're back at the starting slot. For custom ROM users, follow PDA flashing guide for A/B, starting from step 3.
However, if you want to use stock OS, or if you must boot into it at least once, follow the steps below.
Magisk is flashed to ensure that the stock OS boots with TWRP installed.
Now, all we're going to do is wait as it boots to stock.