Free and Open Source Software

As a beginner you could try it with https://yunohost.org

An option which covers a bunch of different experiments: set up PiHole on it (despite the name, it doesn't need to be run on a raspberry pi) then set up a persistent VPN, for eg wireguard, or whatever your router supports, to it from where you are, and then setup your router to use it as your DNS server for your vlan.

Its a relatively simple set of tasks, but they build a good grounding for anything else you end up wanting to run on it.

You can set up a mail server. You can set up something like Nextcloud. You can set up a personal website, or just run a webserver and turn it into a place to dump files. You can set up something like Syncthing to facilitate sharing files between your devices. You can set up some types of Federated services, but in my experience Mastodon is too heavy for a baseline VPS. I needed to augment my instance with additional memory, CPUs, and an S3-compatible object storage provider for about 600GB of user media. Lemmy might work, but I haven't tried running it on a VPS on the open Internet yet.