It doesn't seem to support JS classes neither

If the JS is already minified, you can skip minification with

minifyJs = false

or configure

excludes

for the files that are already minified individually

assets {
    minifyJs = false  // Some js files were not compatible and are already minified anyway

    minifyOptions = [
            optimizationLevel: "SIMPLE", // SIMPLE (default) or ADVANCED or WHITESPACE_ONLY
    ]

    //excludes = ["**/*.less", "**/*.sass"] // excluded from build
}

That's the way I have handled this in the past.

yes I have excluded the one that has the ? operator, but for the one that has classes, it's not minified and it seems classes are not supported either

OK, I think your quick path is the exclude that one, even though it is not minified. And if you have time create an issue on https://github.com/wondrify/asset-pipeline with the details.

note the last release is 5.0.9 and Grails 5.3 uses 3.4.7 asset-pipeline, so I'm not sure if these issues were already fixed in newer versions, but also don't know if I update to 5.0.9 in my Grails 5.3 would break something