@Sashazur  I'm using Android. I'm surprised you don't have the same options on iOS.

Smart actions only let you trigger a single device or a group, so that's expected regardless of platform. Your groups aren't listed since it doesn't sound like you have any. It might be in a different spot on iOS but I attached a screenshot where to create the group on Android.

@Eraseu2 This is really odd. I do have several groups set up in my Kasa Smart app on iPhone. And I just tried the Kasa Smart app on my spare Android phone and just like on iPhone, I don't see those groups available in smart actions - only individual devices are listed. I even made a new group just to be sure. I have verified that I am using the most recent version of the app on both devices.

Do you think it might have anything to do with the kind of hardware you have? The devices I have are 3 Kasa Smart Plug Lites, a Kasa Spot camera, and a Kasa lightbulb. I'm using a TP-Link router but it is not the SB20 and I don't have an Alexa or Google Home or any other kind of smarthome hub on my network.

@Sashazur Try creating a new smart action using a different device, like a switch instead of a smart camera. I suspect the issue might be the triggers from the smart camera might not let you select groups, but the other devices will. Just a guess, I can't test this myself since I don't have a smart camera.

@Eraseu2 unfortunately I don't have a switch! I've sent an email to support. If I learn anything useful I'll update here. Thanks for your replies so far. 

@Sashazur Support confirmed that while the "control with a switch" smart action supports multiple devices, the "motion sensing" smart action only supports a single device. I'm still not sure if my workaround to make three motion smart actions for three devices should be expected to work or not; they didn't answer that yet. Wouldn't surprise me if the answer is no. 

@Sashazur That sounds like an odd limitation, but it matches up with what I suspected based on what you were experiencing.  Hopefully they'll expand the functionality to work more consistently regardless of the device type.

I've been using TP-Link smart switches, plugs, bulbs for years and they've done a pretty good job updating them over time.  It might take some time, but I suspect they'll give those issues ironed out in the future.  In the intirum you might want to try the Google Assistant, Alexa, of IFTTT integration to accomplish certain tasks the Kasa app doesn't allow.  For an example I used IFTTT with my Ring door bell and a TP-link smart switch.  When my Ring Door bell is pressed, it turns on the light by the door inside my house.  After 5 minutes that light turns off (via Kasa Smart Action). 

Using a combination of tools you might be able to make it work the way you want, it just might take a little trial and error.  Good luck.