[K4] 4.0 Compatibility

While works Kirby in 3.9.7, I couldn't get it to work in Kirby 4.0.0-rc.2. In 3.9.7 I see the chunk requests in the network tab in the browser console, but not in 4.0.0. Btw no error thrown. 

I guess it is probably related to the new uploader in K4:
https://getkirby.com/releases/4.0/uploader