hi,
to be honest when it comes to CKE i tend to use js extra config, for example, in the site/modules/InputfieldCKEditor folder i put a file called config.js with
CKEDITOR.editorConfig = function( config ) {
CKEDITOR.config.fontSize_sizes = '8/.5rem;10/0.625rem;11/0.6875rem;12/0.75rem;14/0.875rem;16/1rem;18/1.125rem;20/1.25rem;22/1.375rem;24/1.5;28/1.75rem';
CKEDITOR.config.extraAllowedContent = 'section[id,class]';
};
that will define a custom font-size combo list and, just tried and check this one, allows me to add sections with an id and or classes even with ACF on (new for me as i didn't use them before but it was fun to try 😄) but htmlpurifier off as i don't know how to play with its config, i never did...
i'(m sure it's quite easy to extend up to whatever else you need to allow