The indoor version is a lamp dimmer. I just want a simple on/off outlet. The outdoor version is functionally close to what I want, but it’s big and ugly - something I don’t want inside.

This seems like a hole in their lineup.

A dimmer is a superset, in functionality, of a binary switch. Using the Lutron app or something like Home Assistant, you can treat the device like a simple on/off and drive the device to only values of 0% or 100%.