I've been having great fun recently using Mini PCs using older laptop chips from one of the many sellers on Amazon, installing Proxmox on them, and using them as a host for virtual machines and Docker containers.
First, you put the Proxmox ISO on a USB stick, boot the machine from it, and install it as your operating system. It'll wipe the Windows installation that came with the device. It'll then give you the local network address so you can connect to it's control panel in a web browser.
Within Proxmox you can then easily upload ISO images and create virtual machines from them, like Home Assistant. I always find it easier to manage when you install it as the Operating System version rather than as Docker container, as you get better support for auto-updating and add-ons. Proxmox also supports Linux Containers, or LXCs, which I'd say was a less popular version of the container concept than Docker is. There are several easy scripts to help you launch popular apps in this format.
If you do want to use Docker, then Portainer is also a good option. Create a VM with a Portainer install within it, and you can use that VM to host all your Docker instances with a nice UI.
Proxmox also lets you setup easy backup routines, so you can have all your VMs backup every night to an external disk or NAS.
If you have more than one device you can easily make them a cluster by entering the IP address of your second device into the Proxmox control panel. Then both of them will appear within a single interface. A cluster means that if one of them fails, or you need to switch it off and move it, that the VMs running on it can start on another device. This will work best if you can offload the VM storage onto a NAS.
What seems like magic is moving a VM from one host to another while it's running, without needing to stop it. I was using VMware ESX with this feature many, many years ago. It was magic then and it's magic now.
As well as HAOS, I'm also trying out Immich for photo hosting, Hoarder for bookmarking, ErstatzTV for custom IPTV channels from my own content, and a homepage dashboard so I don't have to remember all the URLs.