So . . . how does one make an external recovery thumb drive of MOJAVE when it already comes pre-installed on a new laptop?

You can get Install macOS Mojave.app via ‎this link and use it as the basis for your thumb drive.

Thanks.

Alternatively you can boot from the Recovery Drive and install a copy of Mojave on the thumb drive. If you have a WiFi connection and even if your Recovery Drive is toast the system will boot from a Recovery Drive on Apple's servers. These days, I can't find much use for a bootable install CD/DVD/thumb drive except to run third party volume repair utilities and the occasion for doing that is becoming ever rarer.

RE: " . . . the system will boot from a Recovery Drive on Apple's servers."

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I am not sure why not, but I did NOT know that . . . Guess one just has to ask, huh?

FWIW (or not), I made the bootable install thumb drive. Can use it with the 2013 desktop - if the need arises, I suppose.

Thinking about it, in enabling bootable install thumb drives, Apple has quietly (almost) given us back the install discs they so ill-advisedly took from us.