I attempted an update similar to the code I wrote for the Jasco 46203 dimmer I wrote about here - [RELEASE] GE/Jasco 46203 ZW3010 Dimmer Switch
The new app only recognizes one button per device now but has a bunch of new values that must be reported as a JSON object. In non-programming terms, Samsung totally broke buttons in the new V3 app update from the way it worked before. 
Hopefully the update linked below works, you’ll need to add it manually from copy paste since I didn’t add it to my repo as it is a test version. It is coded slightly different then other handlers on processing button presses so might still need to fix more if it doesn’t work. This is the dimmer and if it works I’ll do one for the on/off
As I wrote over on the other post, assuming this code works, keep in mind the following:
I was able to make changes to this device handler to now work with the native automations screen in the new Smartthings app. This means you can now setup automations with this DTH for your dimmer switch with single,double, triple taps, and hold without needing to use the smartlighting app or webcore. It will still work with those, but this is a much simpler option for people who don’t want to use webcore or a smartapp, especially for where smartlighting is not available . This is done by programming all the presses either up or down, to “button 1”, and using the new button values of “up_2x" "down 2_x” “up_3x” “up_hold” etc which will be recognized by the new app.
It is a “breaking” change for anyone that was using the 8 separate buttons, so any automation would have to be updated after applying the code update to use button one and the button values. One other minor thing I noticed is webcore is behind the times and only lists pushed and held in its default drop downs, so you would need to do an “expression” and “up_2x” or “down_2x” to continue using the DTH in webcore. (see the linked post above for Webcore example).