The black triangle display when I using Page Break or Horizontal Line. Actually my problem is same with this and this which is displaying an black triangle when try to display an HTML code from CKEditor5 after I save into database. The solution is change some config in angular.json but I not using Angular, I using Codeigniter, AdminLTE and CKEditor5 from builder.
I solved this problem with script:
const blackTriangles = document.querySelectorAll('.ck.ck-reset_all.ck-widget__type-around');
blackTriangles.forEach(item => { item.remove() });