If you open each device in the Smartlife/Tuya app and hit the edit icon it will list the “3rd party controls” that are available for that device.
I have 5 Smartlife devices. They all list Alexa and Google controls. Only 1 lists Smartthing.
In the Smartlife or Tuya apps create seperate “tap-to-run” on and off automations (scenes) for each device you want to use in Smartthings.
In Smartthings run the Tuya integration. Do NOT use the Smartlife integration. (The difference between the Smartlife and Tuya intrigations is that the Tuya integration doesn’t end with an error message. And when you look on linked services the imported scenes are listed under Tuya, unlike Smartlife which is blank.)
When you go back to the main page in Smartthings you will find on and off switchs for each device possibly in No Room Assigned.
They will say they are off line, ignore that for now.
I have been using WebCore with my Smartlife/Tuya devices to overcome the offline issue, and it works good. Reportedly Sharptools can also be used, but I have never tried it.
I create a virtual switch in Smartthings for each Tuya device.
In WebCore I create a piston for each device. The first part of the piston say toggle the “on” scene when the virtual switch is turned “on”. The second part of the piston say toggle the “off” scene when the virtual switch is turned “off”.
I have been using for months with no issues.