As others have said, Linux Security is a very broad topic. But the main thing is keeping your system updated, only install packages from your distro’s repositories, install a firewall and don’t install anything you don’t need should go a long way :)

For example, i use Alpine Linux as a desktop OS. This means i only install packages through apk, from the Alpine repositories. I run apk update and apk upgrade commands every friday. I use Flathub for most desktop software which i also update weekly. (To be even more secure, only install verified flatpak’s). my firewall has no incoming ports open (really not needed on my desktop). And i keep myself updated with the latest news regarding Alpine Linux, and Linux in general. So i am aware of most vulnerabilities as they are published. This is a pretty secure system.

Later on if you want even more security you can start following the CIS guidelines for your favorite distro, but the above should be a good start.

But good security is not just jeeping your system updated, it also means you have good backups in place, in case randsomware hits your system. And then there’s also the monitoring of your system for suspicious behaviour :) But these are far more advanced topics!