If you want to avoid transcoding entirely, a Nvidia Shield is probably your best bet as it supports a few more audio codecs and HDMI passthrough that an Apple TV doesn’t support. That being said, the Nvidia Shield is both more expensive and older than an Apple TV. I would argue that an Apple TV has a better overall experience with third party apps, newer hardware, more up-to-date OS, whereas a Shield works best for Plex/jellyfin.
I bought a Nvidia Shield first to replace a Smart TV and Steam Link and was pretty disappointed with my overall experience. I ended up biting the bullet and getting an Apple TV and the only issue I’ve had is that now TrueHD streams are getting transcoded.
Of course, your experience and desires are probably different so would just suggest looking around for what works best for you.
For macOS, there’s a separate application you need to get magnet links to work. I think this is it but am unable to check currently: https://github.com/Lord-Kamina/Deluge-Magnet-Handler
Life, that is. It would just make life a little easier.