If you are receiving the error invalid args ‘javaVersion’ for command ‘set_java_version’: missing field ‘major_version’ on Windows, it is likely because the permissions on your Java installations are broken.
If you have run the Modrinth App as an administrator, or installed Java as an administrator, you need to make sure you change it to be owned by a regular user. To do this, take the following steps:
Use the "Browse" button next to each Java version to find the Java installation files.
Right click on the
javaw.exefile. It may just be called "javaw".Under "Compatibility", make sure "Run this program as an administrator" is unchecked.
Save changes and repeat for each Java version (21, 17, and 8).
That should fix it!