ASUS offers a dedicated application called the for the Zenfone 8. This is the only legitimate free method.
This is not officially supported by ASUS. Attempting to relock can permanently brick your device. Do not run fastboot oem lock unless you have confirmed it's safe with your specific firmware.
No. Bootloader unlock is software freedom. SIM/carrier lock is network freedom. They are unrelated. To remove SIM lock, contact your carrier.