@The Real GrunfinkI just tested with the default modern.css style file and the error is replicated.
Something in the CSS overlay rendering is causing the header to invisibly overlay the 'clear all' button, deny mouse pointer access to it.
I have replicated it several times in Firefox and Brave browsers.
If I zoom in until the header forces the next content to flow over to the next line, then the 'clear all' button becomes visible.