I just create a bootable usb installer from the downloaded MacOS installer. Choose which macOS version you are using below and cut and paste the command into terminal. Rename the last part to what the name of your USB flash drive is (this will be erased). If you name the USB flash drive 'MyVolume' you won't need to change anything...
macOS Sonoma
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
Ventura
sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
Monterey
sudo /Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
Big Sur
sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
On Intel Macs after rebooting hold down the option key, and you will be able to select the usb installer to boot from and perform the installation.
On the 2018 Mac Mini they have the T2 security setting that you need to first set to allow booting from an external.
Boot into recovery mode (Hold CMD + R when booting, release when you see the Apple logo).
Go to Utilities - Startup Security. Select a user that is admin and enter the password.
Select the radio button for Allow Booting From External.
Hopefully that is everything...