Hardware recommendations wanted for Jellyfin server - eviltoast

Right now I’m running Jellyfin on an old mini-PC with a Celeron J4105. That seems a bit underpowered. I’m using Linux Mint and the installation is with Docker. I’m looking to replace it with something better, so what would you recommend? My criteria are:

  • Easily available (second hand is fine)
  • Budget friendly (under € 500 would be nice)
  • Repairable
  • Upgradable (at least SSD and RAM)
  • Low power consumption at idle
  • Handles all the transcoding stuff without breaking a sweat
  • Plays nice with Linux

I guess my best bet would be some sort of second hand mini PC like they’re being offloaded on eBay by the truckload. But I have no idea which particular models would be a good fit for me. I’m also fine with buying something new, of course.