If you're okay with a (slightly) different tool, may I recommend using GNU Wget2? It is the spiritual successor to GNU Wget. It is already available in the Debian and OpenSUSE repositories and on the AUR
Wget2 provides multi-threaded downloads out of the box with a nice progress bar to view the current status. It also supports HTTP/2 and many other newer features that were nearly impossible to add into Wget.
See my answer here: https://stackoverflow.com/a/49386440/952658 for some more details.
With Wget2, you can simply run $wget2 -i urls.txt
and it will start downloading your files in parallel.
EDIT: As mentioned in the other answer, a disclaimer: I maintain both Wget and Wget2. So I'm clearly biased towards this tool
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