I’m pretty sure the Grid-Connect ecosystem uses the Tuya cloud framework and uses a Grid-Connect branded Tuya app called Smart Life. See https://www.ozbargain.com.au/node/490746
There are a few options for Tuya devices that might work for you. I use a gateway app on a Raspberry Pi to bridge between some Tuya devices and SmartThings. It’s called Tuya Connector: https://github.com/fison67/TY-Connector. It’s not trivial to get it going, but works really well.
Another option is that there been some work at getting a hub-to-cloud integration going, although I haven’t looked into this for a while. Some other systems like HomeAssistant or Hubitat has made some progress, I seem to recall. This work may have made its way into a ST handler.
A third option is to re-flash your Tuya-based device with one of the alternative firmwares that support ST, such as Tasmota. See the Tuya Convert project at https://github.com/ct-Open-Source/tuya-convert
A fourth option is to use the Globe Suite cloud instead of the Tuya cloud (but still using your Tuya/Smart Life login). Global Suite apparently now has support for cloud-to-cloud integration with SmartThings in the new ST app. See New Brands/Devices available on the SmartThings Platform (using SmartThings v3 app)
And finally, IFTTT may provide sufficient integration for what you want to do. I don’t think Grid-Connect cloud supports IFTTT, but the Tuya cloud apparently does.