It’s up to each manufacturer what they choose to expose through any given integration.
The Hue IFTTT channel only allows its devices to be a “that“ not a “if.“
Amazon only accepts sensors as the “if“ for its routines, no switches.
The smartthings IFTTT channel allows its devices to be either an if or a that, so you can actually use that to trigger off of a hue bulb if you want to, as long as that bulb has been exposed to smartthings.
The smartthings/hue integration works well for bulbs, but hue accessories and friends of hue devices are not exposed by the hue bridge to smartthings.
The smartthings/smart life app integration is weird. Most switches are exposed. Most bulbs are not. You can sometimes get around that by setting up a scene in the smart life app and then sometimes that scene will be exposed to smartthings. It just varies by model. But as you’ve noticed, this integration does not always report manual activation of the switch to smartthings. So it doesn’t work as a smart things “if“
HomeKit and Hue have the best integration: you can use Hue accessories or friends of hue switches that are attached to the hue bridge and And then you can have those trigger other HomeKit devices. (I use this in my own home.) but treatlife switches don’t work with HomeKit unless you bring them in through homebridge, which is a whole other platform and requires an additional Bridge device. (Also, “friends of hue“ devices are technically passive devices that don’t listen for network commands, so you can’t turn them on with an automation. So those can only be an “if“, never a “that.“)
A) If you are running HomeKit, it’s easy to have a friends of hue switch trigger other HomeKit devices. Including hue bulbs. And you can have one hue bulb coming on act as the if. But nothing can trigger a friends of hue switch. And treatlife doesn’t work with HomeKit.
B) If you are running HomeKit with homebridge, you can fold in smart things devices and treat life devices, but the technical set up is pretty complicated and you have to have an additional server device. And you still can’t use a “friends of hue“ switch as a that.
C) Ifttt doesn’t really help you with the configuration of devices you are asking about because I don’t believe there is a smart life channel anymore. They used to have one, but they dropped it last year after Ifttt increased their charges. If I’m wrong and it’s opened up again, then that would let you use the treatlife switch as the if and another treat life switch or a hue bulb as that. But you can’t use a hue bulb as the IF and you can’t use a “friends of hue“ switch as either an iF or a that.
D) Smartthings does give you the most flexibility, particularly for the treatlife switches. You can probably use them as a that, but you might not be able to use them as an IF, that varies by model. You can’t use the “friends of hue“ switches as an iF. But you can use hue bulbs as either an IF or that, which is nice.
E) And if you go full rube Goldberg mode you can combine HomeKit, HomeBridge, and smartthings. That would let you use a treatlife switch as an if or a that, a hue bulb as an iF or that, and a “friends of Hue“ switch as an IF. But nothing will let you use a friend of hue switch as a “that“ because their technology does not allow them to receive commands. Just send them. And the solution is technically pretty complex to set up.
So as always, the first rule of home automation applies: “the model number matters.“
There are other devices that could give you a similar end result without all this craziness just by choosing devices which do all work with the same ecosystem.
You didn’t say what country you are in, and the device selection does vary. But instead of treatlife, I would look at meross switches if you want Wi-Fi devices: they have a much better smartthings integration. Each switch can be used as an IF or a that and they do report manual activation.(By the way, they also have a good HomeKit integration.)