CSS commands don’t affect children elements. The selection blocking is only applied on the element specified and not to the ones it may contain. In Bubble, a text element is a div but the actual text is inside a child div so it’s out of reach for the user-select rules.
To also affect descendants elements of the one on which you apply the rules, have an “*” to tell the CSS engine (also, include all children!). So this should work:
And using Classify, version 2.0, you would write in the ID field: {addClass: "noselect"}.