This. My Mac has 16GB but I use half of it with a Linux virtual machine, since I use my Mac to write Linux (server) software.
I don't need to do that - I could totally run that software directly on my Mac, but I like having a dev environment where I can just delete it all and start over without affecting my main OS. I could totally work effectively with 8GB. Also I don't need to give the Linux VM less memory, all my production servers have way less than that. But I don't need to - because 8GB for the host is more than enough.
Obviously it depends what software you're running, but editing text, compiling code, and browsing the web... it doesn't use that much. And the AI code completion system I use needs terabytes of RAM. Hard to believe Apple's one that runs locally will be anywhere near as good.
Not sure about jellyfin, but I assume it uses ffmpeg? The M1 is fast enough that ffmpeg can re-encode raw video footage from a high end camera (talking file sizes in the 10s of gigabyte range) an order of magnitude faster than realtime.
That would be about 20W. Apparently it uses 5W while idle — which is low compared to an Intel CPU but actually surprisingly high.
Power consumption on my M1 laptop averages at about 2.5 watts with active use based on the battery size and how long it lasts on a charge and that includes the screen. Apple hasn't optimised the Mac Mini for energy efficiency (though it is naturally pretty efficient).
TLDR if you really want the most energy efficient Mac, get a secondhand M1 MacBook Air. Or even better, consider an iPhone with Linux in a virtual machine - https://getutm.app/ - though I'm not sure how optimsied ffmpeg will be in that environment... the processor is certainly capable of encoding video quickly, it's a camera so it has to be able to encode video well.