A huge second to this!

Ironically I just found this post as I am attempting the same thing.  I exclusively use Kasa smart lights, as they provide many more functions vs just "on" and "off".  I use Home Assistant to run everything.  The problem I have is mostly when guests come over.  They want a simple switch to turn lights on or off; they don't want to have to grab a phone and use an app.

A smart switch (light what you already offer), but with a decoupled mode would be IDEAL.  It would leave power on to those already smart devices, while still allowing it to control the lights (either directly similar to the already available grouping in your app or through another 3rd party, such as Home Assistant).

Maybe this is as easy as a firmware update?

  @brothapig Aquara light switches already have this feature.  Better get on it guys you are falling behind.

  @BDJones I was trying to figure out a similar problem I have. In short, I think it is definitely possible. Here's how it worked in my setup.

Tested this on my kitchen light switch. Typically, my light switch is connect to both black line/load cables and the neutral return. I also have two under-counter light strips that run off of AC power and have a smart controller on them. I use a Google Home routine to turn on those strips whenever the light is on and another to turn them off when the kitchen light is turned off.

I tested what you are looking for by disconnecting the black wire that leads to the lights (as opposed to the black wire that comes from the power source / breaker box), being sure to cap both end of the cable with a wire nut (for safety - this is still a live wire, so you need to cap it). So now, I have a light switch that is getting power and communicating over wifi, but not connected to the main light. When I turn on the switch, the google routines still run! (and the kitchen light does not turn on).

There is no "decoupled mode" for this, you just have to choose not to wire up the actual light.