Questions about TL-WPA8630P Powerline Kit

I don't have exactly the same feces as you - but a relatively old one from TP-Link. I was able to pair it without any problems!

Remember most "computer" use is bursty. Streaming is consistent. So if all devices (connected via ports and WLAN) are pulling asynchourous, you have little to worry about. If all are pulling a 4Mbit/s stream from many devices, you probably need to worry about your external broadband provider.

On toppreise.ch there are a few sellers who only offer the extender, but at the same price as the kit. But there is no photo with any of the suppliers, so maybe it is also the kit but declared incorrectly.

On Amazon.de it is also offered separately but with a lower price (80€). Just search for "TP-LINK TL-WPA8630P", which was my first hit.

I don't know why only the extender is not offered properly

Unfortunately, this is "normal" and due to the respective power cabling.
Depending on the power grid in the building / number of connections / sockets etc., LAN via Powerline seems to work better or worse. I also had this kind of behaviour with Netgear Powerline.

The ideal solution is therefore to set up a "separate" (LAN) network for it - if possible. Otherwise via WLAN / APs.