Workflow SDK with JS API 4.x

Hi, I'm new to the workflow SDK. The SDK doc says the ArcGIS API version for the activity SDK can be changed by updating the @types/arcgis-js-api as below:

"devDependencies": {

"@types/arcgis-js-api": "4.15.0",

...

},

?

After that, do I need to do anything else in the code? I've tested my custom activity in HTML5 viewer but seems it still use the 3.x API. thank you.

?