But Element pickers are not a good way to create cosmetic filters anyway, so nothing of value is lost, if you want to do it in a better way use DevTools, since you can see everything and properly make your cosmetics to be cleaner and better.
In general, the built-in element blocker will work perfectly fine for most users as it is simple and straightforward to use. That said, Emi is correct and the option was removed due to privacy concern when using the element blocker in Private sessions.