I’ve seeded on a router from 2013 with 128 mb ram. Transmission client runs on openwrt. It was running all the time as an access point anyways I think using around 4 watts of power. 128 mb of ram was cutting it rather close and I had to add a swap file but the system was running stable. If you have an old router compatible with openwrt and an USB port to add an external hdd you can build yourself a very cheap and power efficient seedbox.I think the xiaomi mir3g has the same chipset at double the ram. Those can be bought for around 15-20 Euros used in my region.

Rockbox runs on apple ipods. Best thing to do is always buying a device compatible with open source software if you plan to use it fir years on end.

I bought one of those used for my daughter a couple of years ago. It was quite the hassle to replace the apple firmware win with rockbox, but it’s been working well since then. It’s copy and paste mp3s now instead of using apples spying bloatware just to get a few files onto the device. The battery is not great but still lasts a couple of hours after 15(?) years.

There is also bcl on fdroid, requires no dongle but root access, as it just changes some lines in a config file on the root partition.