Had several old PCs over the years from relatives, but either gave them to other people or threw them to the trash because I didn’t see the usefulness back then…
Right now all I have is my PC (which I guess I could put VMs on), and maybe a few phones (maybe just because they kinda are there like backup phones), which I couldn’t find how to root, if these are of any use with unrooted Termux.
Do you have any advice about it? Should I start with my PC with VMs? An unrooted phone with Termux? Try to look somewhere that is gonna get rid of PCs or something? If so, where?
What do you want to practice? Just general sysadmin stuff? Networking? Clustering? Horizontal scaling? All of the above?
Old PCs are just Debian servers waiting to happen. Depending on their specs, you may be able to do VMs or you can utilize container frameworks like Podman, Docker, or LXC to deploy individual applications or application stacks. Or you can just bare metal install anything you want.
Years ago, I bought a batch of 16 Wyse thin clients on eBay for about $15/each. These had 4GB SSDs and 2 GB RAM, so I upgraded about half of them with 64-120GB SSDs (whatever I had lying around) and 8 GB RAM. Thin clients can usually be found pretty inexpensively and are pretty power efficient, but they’re not performant workhorses. They’re great for practicing networking, VLANs, system orchestration (e.g. Ansible, Cockpit) application clustering and horizontal scaling, diskless workstations, setting up a demo office server and workstations, and even VMs if you’re just practicing; they’re a little underpowered to run a lot of VMs, but you can certainly run a few small ones just to practice managing them.