Find your thing.
For me that’s been different things as I’ve gone through life. Currently in my 50s and enjoying riding a motorbike at weekends. When I’d ridden all the local roads so many times it was starting to get boring, I added another layer and am now riding my bike to every Village in my county. It’s going to take a while, but has given another layer of interest and purpose. Many people won’t understand why it’s interesting to me, and that’s fine, they don’t have to. Finding what works for you is half the challenge.
BTW, if you’ve got depression, then finding happiness without resolving that is really, really difficult. Been there and absolutely everything felt bleak and pointless. Fixing that is the first step.
It’s fine, but not going to be the cheapest.
Cheap to buy: Any old PC desktop, really. Most will run linux and windows fine, depending on what you want. Anywhere from free to £100. If you have an old desktop or laptop already, use that to start with.
Cheap to run: Any mini PC. I run a Lenovo ThinkCentre M53 for low power duties. Cost £40 and runs silently at 10watts, idle. (I have a secondary, much beefier server for other stuff that runs at around 100w which lives in the garage)
But plenty of people do run mac minis as home servers, often on Linux. They’re fine - just do your homework on the CPU ability, how much ram you can add, and whether you’re okay with external disks if you can’t fit enough inside.