Is Mac Mini suitable for self-hosted server?

I bought a M1 Mac Mini second-hand and it's great for home server purposes. Like others have said, you'll be using containers a bunch, so bare metal doesn't matter quite as much as it used to. They're power efficient and offer good performance. If you're in the Apple ecosystem, there's a bunch of other benefits to having a Mac set up as a server (e.g. content caching for updates/iCloud content).