Hi, I've discovered another solution for myself. Since I have a mobile phone contract with a large data volume, I have coupled my Gear S3 to my hotspot. So Spotify works over the clock again, but only over the WiFi hotspot of my mobile phone. This should help to bridge the time to the official solution of the problem by Spotify. And I don't have to install an old version and make sure that it doesn't update itself again automatically.
It took half a year, but my Gear Fit2 Pro updated it's Spotify app couple hours ago and the Remote mode works now! Version number of my Gear's Spotify app is now 1.1.28 (I think the old version number was 1.1.23).
Hopefully the update will be available on other Samsung smart watches/activity trackers too!