Options to adjust under adsl vdsl connections?

Active downloads and threads per download should be able to set higher by user.
I don't see any reason to lock the number to 1....
Even it's "slow" connection for ur understanding but it should be set by user for daily using with no problems.

I did not really understand your question.

The software does not account for ADSL communication hardware, etc.

If the internet speed is too low, the multiple threads are slowing down the download. The total download speed is significantly reduced, many errors, re-sending requests, connection losses, etc.
At low connection speed, the only reasonable way is to set up 1 stream for download and let it download the file correctly.

You can do the same manually - set Fast download, set 1 thread per download and set connection timeout ~180 sec.

Every other download manager like idm . xdm;can set multi connections or threads . Why u have to lock the nummber to 1? It should be able to adjust bu users i think.