I have now received an e-mail in response "I plan to replace the IB4 with the Fritz 5590" (not visible here)

My personal opinion is that it only makes sense if an alternative provider such as Init7 or SolNet etc. with Zattoo TV is running behind it. With a FRITZ!Box you leave the My Swisscom eco-system. The customer saves a lot of money, gets more performance for less francs per month and supports Swiss SMEs. The 5590 runs smoothly, but if the latest technology and cancellation periods at the supplier also play along, then my tip is the 5690 https://www.iway.ch/ueber-iway... and yes, iWay is also a great Swiss SME cheaper than Swisscom. The 5690 should be available in the summer, from my experience with AVM it can also be December 😉

Counter question, what is meant by WLAN boxes? Repeaters? Router?

The FRITZ!Box 5590 XGS-PON is a Swisscom certified router: https://www.swisscom.ch/dam...

The question now should rather be, what is it supposed to replace? The Swisscom router? If so, what technology does the existing fibre optic connection have?

But as already mentioned, the 5590 is certified by Swisscom and therefore also supported.

I tried to connect this box to Sunrise, but unfortunately it didn't work.