And it works, I see the traffic information drawn. But I was trying to style the layer a bit more. And since - in my understanding - the v5-version of the SDK is based on the Mapbox GL JS library, I was browsing through their documentation to see what options I had (since it’s not described in the v5-documentation, right?)
Error: layers.10551905.paint.line-cap: unknown property "line-cap"
at Object.un [as emitValidationErrors] (bundle.js:14)
at Te (bundle.js:14)
at r._validate (bundle.js:14)
at r.addLayer (bundle.js:14)
at A.addLayer (bundle.js:14)
at t.<computed> [as addLayer] (bundle.js:14)
at bundle.js:2237
at Array.forEach (<anonymous>)
at drawRoads (bundle.js:2236)