I know now that Room Lighting is out, Groups & Scenes has been deprecated. My question is how? In my example, I have a lamp in my basement office that has 3 Sengled Zigbee bulbs in it. Before, I had a group for these called "Basement Office Lamp". I would like to expose a "Basement Office Lamp" device so I can use it in Google Home and Homebridge. How would I do that?
I know I've heard people say Groups & Scenes will continue to work, as-is, but I'm leery about continue to use something that has been deprecated, and I'd rather ask if there are any other recommended solutions here?
First, Groups and Scenes was actually "un-deprecated," so you can still create new instances even if you've never used the app before (and even deprecation didn't meant that it would stop working or that you couldn't if you already had it). It's unlikely to receive new features or much/any further development, with Room Lighting being the more-featured suggestion as a replacement, so that much is at least true.
To answer your question, what you need to do in Room Lighting is create a name for an "Activator Device" at the bottom of the main page:
This is like the Group or Scene activator that gets created automatically (with the name of the group or scene). Commanding it will command all of the devices in the Room Lighting "group," and similar to Groups and Scenes, there are a few options that control exactly how it works. See here for more: How to use Room Lights for Groups
Cool but with the activator device, that’s an on/off switch right? In this case, I want to be able to dim this group. Is that possible with RL?
Once you add/create the Activator Device in RL, it's a device in your Device list -- there are seevral different device-type flavors you can change to if you don't like the default it picked for itself.
If it doesn't create itself as a "Room Lights Activator Dimmer", you can just change it to that (or any of the other "RL Activator [type]" options.
Room Lighting is crazy configurable (which is great), but the downside of having so many options is that it's not exactly intuitive. But if you're patient and willing to play around, you can do some really cool things that would otherwise require numerous disparate rules and apps.
No, the activator is a device that matches the type of devices in the group. If you have color bulbs, the activator is itself a virtual color bulb, Or, dimmer yields virtual dimmer, etc. When the activator device is commanded with setLevel, or setColor, on on/off, the devices themselves get the same command.
Sweet! Now it’s making a lot more sense! Is there an equivalent to the “group on” to prevent popcorn effect?
Do you mean Zigbee group messaging? That's what could be used to prevent the "popcorn effect" in many cases before -- a single group broadcast instead of a command to each bulb. If so, that is on by default (if supported) unless you turn it off. You can see a screenshot of this in the post I linked to above, or it's under "Additional Options" for "Activate Lights Options."