Go to r/homelab and r/selfhosted. Get a mini-pc, pick either Debian/ubuntu, or a flavor of Redhat. Build yourself a “server”.
Make it headless.
You can get a free Redhat account, 16 feee licenses? And a lot of other free tools. Or use Rocky/Alma/Oracle. There are some differences with “subscription manager” on Redhat.

You can use a laptop to remote-administer the server. Do not depend on a GUI for everything you do. You can use a GUI/desktop on your laptop simply to have a half dozen terminal windows, and an IDE, and web browsers open. A lot of stuff doesn’t have a GUI. Setting up a web server, it’s mostly editing files from a command line.

You’re going to want to become proficient with VI/VIM. You might also pick up on an IDE… VSCode has some learning curve, but there’s TONs of help from VSCode, various howto sites, and YT. Much of it will be in relation to GitHub and version control. And you can do remote sessions to your server with VSCode, so your VI skills might not be quite as important. But from a foundation, using VI is a daily thing for most people.

Start doing stuff at home. See my first line about those 2 Reddits.

Go ahead and do some Linux cert classes. And practice. And take the tests.

My world, it’s almost all Redhat Linux, or the similar flavors (Rocky, Oracle, or Alma). Redhat (enterprise Linux, or EL) is different, but in some ways similar to Debian/Ubunu.

It won’t hurt to learn a bit of either of those major distros. It is going to pay off to at least have an idea of the differences.

Most of the companies and people I know use Ubuntu or Mint for our laptops. But there are quite a few Macs, and Windows people.

You can run a server with a bare metal Linux distro, and then run a VM from another distro. That’s very common. You can keep adding VM’s of almost any distro out there.

You might run into BSD. There are some flavors of BSD. It is a bit different. It’s out there, and can be a bit hard to handle at first. It goes back a long time when there were 2 flavors of Unix. You can Google that history, just read the Wikipedia entries and know that it exists.

Learn GitHub as a source for open source software. I’d also learn some bash, and learn Python or Go. Use GitHub for version control, see my bit above with VSCode.
You could also look at the CNCF landscape page. It’s … kind of a reference for a lot of cloud and open source software. Huge rabbit hole for you right now. Bookmark it. Know that it exists, and when you hear buzzword-sounding names of pieces of software, go look them up, and you’ll get a notion of what they do, where they’re used, and a sense of their popularity.

Which reminds me. Open source software will have a License. Licenses exist for various reasons I won’t go into.. I like MIT and Apache. But there are quite a few others. Some of them are more restrictive than others. You can Google those licenses and get the gist of what they say. If you were to start a business, knowing all of the details on licenses will become important. Running someone’s application at home, tinkering, learning, you won’t likely violate a license.

Learn containers. How to read a dockerfile, how to build and deploy a container. Understand that there are reputable sources for pre-built containers. And that there are disreputable sources for containers.

Learn some of the more esoteric things like storage and networking for containers in various ways. Tons of people use the default bridge for development and testing, but servers, you might want containers and VM’s to have their own IP address.

You’re going to learn how to use a Linux package manager, and do installs, updates, upgrades and such along the way.

I’d also install qemu/kvm, learn how to do VM’s. Build an image from an ISO, and start that image as a VM.
Host other flavors of Linux. Or possibly even Windows. Hardware and BIOS. You might not have a choice of hardware when you get a job, but you’re going to have to learn to figure out what you’ve got, and how it’s set up. Lshw and lspci,nproc, dmesg are useful to look at. Learn how to tail a log file while you’re doing something, I use IPMITOOL all the time, especially on new hardware, or hardware I’m not familiar with.

With VM’s, you can use a GUI like virt-manager, but I think it’s better to use the CLI tools (virsh, virt-install, etc).

Command line interface is powerful. GUIs tend to be watered down, or they don’t exist. They have value for a home user, but in the corporate world, if you only know how to point-and-click, you’re going to be left behind.

Learn to monitor containers, the hostOS, and VM’s. Prometheus, node-exporter, Grafana is a pretty good start.
There are other ways, but with those three, you could be running in under an hour. GitHub is littered with docker-compose stacks for monitoring.

Learn to subnet, switch, and route. And DHCP and DNS. You won’t have to be an expert. It takes years to for that stuff. Buy a cheap router and switch, learn to pass VLAN tags to your server, build Linux bridges, or Openvswitch, and build containers and VM’s with their own IP, hostname, DNS entry.

You could learn a bit about SQL, and no-SQL. 10 minutes of googling, reading Wikipedia pages. And if you want, set up a database server from a container. Or a LAMP stack.

The hardest parts are typically storage, networking, and security. Every company will do different stuff. You can easily do a career on one of those 3. You don’t have to be an expert, just understand the fundamentals, and know that there are 4 billion ways to do stuff.

Networking, I mentioned above. Storage, I’d learn NFS, Samba, and eventually … maybe… ceph.

Security, I’d look at freeradius and ldap/ldaps as a foundation. And certificates, and public key exchange.
And a metric crap ton of other security stuff will drop on you like a ton of bricks. Security is an incredibly deep rabbit hole.
Everyone hates security, but it is absolutely required for everything you do.

Classes tend to gloss over a lot of those 3, they give you the basics, and they do a lot of hand waving about other ways to do stuff. To me, classes and tests are enough to get functional, but when you land a job, that’s where the real learning happens.

Good luck.