Is this a possible Solution? (see details below)
in short:
More details:
After reading all comments in this thread (and wondering how on earth it could be true that it is up to us (the paying customers) to solve a problem that obviously Microsoft and Telekom seem to have for years now), I made some tests to figure out, which of the suggestions spread over all posts might indeed deliver a ‘solution’.
Whereas: I don’t consider what I found out more than a (at least for now) functioning workaround, IMHO it’s up to Microsoft and Telekom to provide a solution that works for every user, not just for those who are willing to mess with their router configuration.
Here’s my configuration:
- XBOX X, per LAN cable connected to Fritzbox 7632SL, 100 Mbit VDSL Telekom
- DNS-settings on XBOX: automatic
- DNS-settings on Fritzbox:
- primary IPV4: 1.1.1.1
- secondary 1.0.0.1
- primary IPV6: 2606:4700:4700::1111
- secondary IPV6: 2606:4700:4700::1001
- wether I have google or CloudFlare as second DNS makes no difference
What I’ve tried to get here:
- Google DNS in XBOX-configuration
- CloudFlare DNS in XBOX-configuration
- just Google or CloudFlare DNS IPv4 in Fritzbox
- Google DNS IPv4 and IPV6 in Fritzbox
- CloudFlare DNS IPv4 and IPV6 in Fritzbox
With all the above ‘’ configuration, in FritzBoxs’ Online Monitor it looks something like this:
Apparently nearly no data at all is received!
With CloudFlare it looks like this:
Finally the Sim is using the bandwidth available!! 
Loading times of all tested options (missions, freeflight, challenges) are quite good, as the screenshot show it now even might make sense to go for a faster internet connection, since the Sim seems to use the available bandwidth.
Please reply to this post and let us know if this configuration works for you too (even for PC-users?).
If so, this might be important information for Microsoft and Telekom to find a stable solution.
In any case:
I suggest Microsoft and Telekom shall have some serious conversation!