adoptium.net VS GDLauncher

1.18 requires Java 17. (Java link if you need it)

Note: In order for JarFix to work, you needed add all options when installing Java (Picture).

Did you actually install a Java Development Kit? Because this sounds like you only installed a text editor. You can download it here: https://adoptium.net/ (download the latest version for your OS and install it)

Try this https://adoptium.net/

Make sure you have Java fully installed (select all components when installing). Link to Java download if you need it: (Link)

if you downloaded Java from adoptopenjdk/adoptium/temurin/whatever they call it now, you do have it.

I had the same issue and I fixed it with downloading openjdk 17. you can download it here https://adoptium.net/

Which was recently rebranded as Eclipse Temurin

if they are using Windows, have them reinstall java https://adoptium.net/

e.g https://adoptium.net/

I used to use GDLauncher, but I would not recommend installing a launcher that lets issues like this one go by for almost a year without being fixed: https://github.com/gorilla-devs/GDLauncher/issues/1288

Skip all that manual install crap - https://prismlauncher.org/wiki/ or https://support.curseforge.com/en/support/solutions/articles/9000196904-creating-a-custom-profile or https://github.com/gorilla-devs/GDLauncher/wiki

Another way to make it easy, a bit less easy than the prior but a bit more customization - https://github.com/gorilla-devs/GDLauncher/wiki

The latest GDLauncher beta added an option to allow users to manually download problematic mods. You can get it here (click the Assets dropdown) or wait a few days for it to be released as a stable version.

I would have recommended GDLauncher until this happened to me last week: https://github.com/gorilla-devs/GDLauncher/issues/1288

Maybe give a different launcher a try, I use GDLauncher to run modpacks

maybe you could try GDlauncher it allows you to

Personally i use GdLauncher since it's really simple to use, it also automatically installs open jdk for you, something that basically makes the game run better than normal java, and can still manually download mods that have third-party downloads disabled.

Which other launchers could I use instead? – The shunted devs have established PlaceholderMC as a temporary official replacement. There's also ATLauncher, GDLauncher, and PolyMC itself was a fork of MultiMC.