Update to my download issue:

Problem fully solved ! It was an issue with my DSL conection from German Telecom.
IP packets get lost and cause slow downloads.
As workaround I used Cloudflare Warp this helped immediately.
I have now restarted my DSL connection via service portal Telekom and after reset and restart the download works as expected .
So issue was definitiv located at German Telecom and a Reset of the DSL connection at Service Portal solved the issue.

BR

Stephan