Hello Imhotep,
I don't have a definite answer to this but I could imagine that it's country-specific... I found a thread from Samsung, but not related to Switzerland (https://us.community.samsung.com/t5/Blu-ray-DVD-Players/How-can-i-watch-Amazon-Prime-video-on-my-UBD-K8500-blu-ray/td-p/158293).
Greets
I have connected this player with LAN and there is no problem streaming from the NAS (QNAP). I have now tested it with wifi and it also works. With Full HD videos it runs without problems, with 4K video I had a short dropout, but then there was no problem during playback (router is in the same room).
I think you are using a modern router that also provides the 5G network, which is the first choice for media streaming. The wifi adapter of the UBD-K8500 can handle it.
Nevertheless, you should try to connect the player via LAN because of the high data volumes or use powerline adapters as an option.
You probably have a 4K TV that also supports streaming - just try it out, then you won't need to take the diversions via the player.
It depends on the medium/file format you want to play. With 4K Ultra HD Blu-ray, the content is "real 4K". So when buying blurays, look for the indication "4K Ultra HD", such as with the following product: Deadpool 4K
According to the respective question in german: UHD Blurays are codefree, Blurays are region B and DVDs are region 2. So european region for Blurays and DVDs. -> https://www.digitec.ch/de/s1/QuestionAndAnswer/welche-region-codes-hat-dieser-player-uhd-ist-region-code-free-das-ist-klar-aber-ist-auch-blueray-un-21726