I had an S4 and it worked great on the HD TV. The S6 never connected properly, I assume because it has a higher resolution. With the 4K TV I have a direct connection.

The upscaling of the 1080p HDMI signal to 4k is done by the processor of the 4k TV alone, so it has nothing to do with this stick. Only from HDMI version 1.4, but better 2.0, does the native 4K signal reach the TV.

I tested the adapter on my LG '49 4K. The picture often had graphic artefacts and it seemed to stutter very slightly. If I change the setting to HD 1080p, the graphics artefacts disappear and video playback runs smoothly.

Technically, I cannot answer this question, but the part was created before the 4K era. However, Microsoft presented a successor for this adapter a few days ago. It would probably be better to look for the successor.