The ability for individual users to run custom groovy smartapps in the smartthings cloud is what is dead.
You can still have custom SmartApps, but you have to host them yourself.
And there are still a few official smartapps, provided by Samsung, which includes a new version of smart lighting.
See the community FAQ for more details. SmartApps are covered in points 10 and 11.
FAQ: I have no idea what Edge is. Is that a new developer tool? (2022)