I don’t know what the best way is to do this now because I can’t use the new 2021 app very well, it’s not voice navigable. But have you tried using SmartThings scenes for this? You can group a bunch of lights together and specify the dim level for each one. Then refer to that scene by name.
You can’t change the levels dynamically, but you couldn’t with the old smartthings routines, either.
So for example, at our house we have one called “bedtime scene” which turns off a bunch of lights and turns on the hallway night light to 25%.
We have another one called “good morning scene“ which turns off that nightlight and turns on a couple of other lights.
And of course the classic “movie scene” which turns off some lights and turns on some others at 25%, and the entry light at 50%.
The thing is that a scene is just a snapshot of a moment in time. So you activate them, but you don’t turn them off. You need to have a separate scene that turns everything off. Or a group.
So it’s not quite as intuitive as what you’re describing, but it can work pretty well as long as household members can remember the name of the scenes.
To use a smartthings scene in Alexa you can say “Alexa, turn on bedtime scene“ but we prefer to say “Alexa, activate bedtime scene.“ It just seems more natural to us. And I think it helps people remember that they won’t be able to turn the scene off again.
There is a caveat:
For security reasons, Alexa will only support Scenes with lighting, switch, and thermostat devices.
What that means is that if you have a smartthings scene with a lock in it, Alexa won’t use it. But for lights, your smartthings scenes should be discovered automatically by Alexa just like your devices are.
Again, I don’t know if there’s a better way to do what you’re asking for, this is just what we use.
Here’s the official support page on creating scenes, but I don’t know if it’s up-to-date: