UnsatisfiedLinkError: Can't load library libawt_xawt.so (Headless Java on Linux)

What it looks like in the log

java.lang.UnsatisfiedLinkError: Can't load library: /usr/lib/jvm/java-17-openjdk-<so>-1.fc38.x86_64/lib/libawt_xawt.so

How to fix it

1. Install the full (non-headless) OpenJDK package for your Linux distribution so Java includes desktop GUI libraries—for example: 'sudo dnf install java-17-openjdk' (or java-21-openjdk) on Fedora, 'sudo apt install openjdk-17-jre' on Ubuntu/Debian, or 'sudo pacman -S jre-openjdk' on Arch.
2. If you use a Wayland desktop session, make sure XWayland (e.g., xorg-x11-server-Xwayland on Fedora or xwayland on Ubuntu/Arch) is installed so Java X11 windows can open.
3. Verify that the file you ran is actually an installer: standard mod jars like 'iris-mc1.20.2-1.6.10.jar' are not installers and belong directly inside your '.minecraft/mods' folder rather than being launched with 'java -jar'.

Check your own log