The core files are read-only. You can layer new system applications, but it’s not as easy as just installing a package. Most things are handled via Flatpaks. So the base is solid and you can’t do much to really ruin the stability.

There is a learning curve, as it’s different than normal distros.

Here is a decent read up on it: https://www.linuxnest.com/what-is-an-immutable-distro