Newer Java versions generally work out of the box, it's not as bad as the Java 8->9 compatibility gap. The change that is sometimes needed is to manually update one or more libraries the game depends on (like ASM) as those usually have a maximum Java version they support at any given time. This has to be done in the mod loader itself, it's not possible to upgrade the library with a mod alone. Some launchers like Prism also allow overriding the versions of libraries manually, but it requires knowledge of what file to change and where.

There is nothing I can currently do to make that process easier in ModernFix itself.