Add elements in Mosaic widget

[admin]

Can be done via Custom CSS in Setting & Themes:

Code:

#u-352daf4e75651dd160ec9aed807ccf02 div[data-index="2"] .datetime {
  pointer-events: none;
}

Use browser dev tools (F12) to find out custom widget ID and index of the element that you want to make read-only: