Have the same problem, use Telekom 100 MBit/s, download rate breaks down in the afternoon, while being at consistent 100 MBit/s at low demand times.
Pointing fingers towards Telekom will not do it, in my opinion. My Telekom connection works just fine with all other applications, including MSFS 2020.
Changing DNS didn’t help at all.
Packet Loss Test shows zero loss with servers in New Jersey and UK, latency below 100 ms. It really should work with that. But it doesn’t.
It’s very likely not a Telekom problem, but a Microsoft infrastructure problem.