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.