with some magick and wizardry i was finally able to make qbittorrent compatible torrent which downloads from webseed (http server)
there is this issue that you need both webseeded file address as well as .torrent file. magnet link in theory supports both, but not really in qbittorrent.
i imported magnet link
then i imported previously created .torrent file, which adds some data from torrent file
then i exported .torrent file
finally i deleted existing torrent from transfer list
and imported new torrent file to see it works
this torrent now has webseed, so it can download from http source in addition to bittorrent peers. works in qbittorrent:
https://files.catbox.moe/5xsw69.torrent