I managed to change the theme breakpoints by adding my own _breakpoints.scss in themes/my_theme/css, and replace the import in all pages.
The breakpoints are Ok and can use my custom ones but I have no luck making the “@mixin for-mobile” and “@mixin for-desktop” mixins to use my breakpoints. It reverts to the core breakpoints.
Is there a way to override a core mixins at theme level?
Thank you.