Is there a shortcut to "Switch User" from the Lock Screen in macOS Mojave?
There might not be a ready made one - but you can write your own!

This link explains how to apply a shortcut to some applescript that you have already written.

If you are not familiar with Applescript (new skill to learn! :)), you could check out this link where there are a number of other suggestions (including a user switch script - but your password will be in plain text).

Let us know which one works for you.