There are no download managers because it is unlikely you are still on dial-up in 2026. There are no torrent clients because they would consume a lot of traffic and battery (unless they are leech-only that would break the whole torrent ecosystem).
F-Droid
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
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Libretorrent is not buggy, and it's actively maintained. Open up an issue on its repo if you have one.
I agree that LibreTorrent may be buggy at times but is by far the best tool for torrents on the platform. Also Aria is great, but not as a torrent client, but as a download manager it easily beats most other tools that I've used as a replacement of the default mechanism (especially the speed is incomparable, when you can increase number of connections).
I think that's because Android has never been particularly popular for the desktop, much less server, so for most use cases, where you want perpetual uptime, you're going to run torrent on a desktop or server, which you can manage with an Android FOSS app like transmission remote on your phone or tablet.