Which internet solution do you recommend?

Thank you and for your answers and the little digression on the subject of OT.

Edit: if also answered my question, thanks to him as well, although I only understood "train station" ops:

Rhenish greetings

In general, there is noise and interference on the line (e.g., coupled in via poor shielding) as well as the useful signal. Both have a certain strength. The longer the cable, the weaker the useful signal becomes at the receiver at the other end. For good transmission, the useful signal must be clearly stronger than the interference. There are several ways to achieve this. A shorter cable or a better one (larger cross-section) means less attenuation of the useful signal. Better shielding means less interference. Both result in a higher signal-to-noise ratio (ratio between useful signal and interference). Therefore, there are different options or adjustments. This was explained in a very simplified way for laypersons, so please don’t stone me!

Related to the current usage, would it make a big difference if the cable had "only" 850 MBit/s instead of the specified 1 GBit due to a kink???

A cable is not a garden hose.
There are 8 wires inside the network cable. Each one is necessary to achieve a transmission speed of 1 GBit/s. If one wire is broken, that's the end of it. The standard to achieve 100 MBit/s only requires four of the eight wires. All four of these are also required to enable data transmission. If one of these is broken, Ethernet is definitely done for.

I don't believe that Peanuts meant a ruptured blood vessel by "Knick".

I don't think Peanuts meant a vein rupture with "Knick".

Of course not, if the hose is torn into 2 pieces, nothing would work anymore. I meant that the veins themselves are okay, but for example the shield has a tear...

Of course not, if the hose is torn into 2 pieces, nothing would work anymore anyway. I meant that the cores are basically fine, but for example the shield has a tear...

Okay, I understand. But that is an unlikely fault pattern. The tear in the foil shield (if there is one – depending on the cable type) naturally leads to more interference at the damage site. The impact is likely to be minor or not noticeable, especially within the permitted cable lengths, unless a baby monitor and microwave are right next to each other. If you manage to tear the foil inside the cable, you likely have a problem with the cores rather than from the damaged foil.