Mac Mini 2018 Reboot Loop?
Wiping the entire internal storage may have been a bad idea, as it also contains the Recovery Partition, and some 'keys' used to authenticate Secure Boot. (Also note that by default, you can't boot to a USB external: you need to set the Secure Boot options to allow that.)
https://support.apple.com/en-gb/HT208198
Your best bet is to install it from another Mac using Target Disk Mode.