Thanks @JDRoberts and @Terri_Baker.
Cliff notes version:
For Google Home Routines: Add a Virtual Switch via SmartThings App → Menu → Labs.
For Alexa Routines: Add a Virtual Device via Virtual Devices V2 → vEdge Creator V2.9 (Follow Instructions Steps 1-3 posted here)
Both are super easy to install and configure.
I got both Google and Alexa “speaking” and “doing things” triggered by my Automation Routines in my SmartThings app.