have you tried long pressing on the text line?? It should pop up automatically. I'm not sure if it works in every mode though like say, if you are using the floating keyboard feature or what not, but it should be visible at the top right of your keyboard if using the standard.
I actually switched from the same phone to the a21s and am very bothered about the clipboard not being a keyboard setting I can enable. When looking for it on the three dots the only things displayed are search, translate, text editing, modes and keyboard size. When copying text, there also isn't a clipboard setting to pop up either. The clipboard setting is practically nonexistent on these new phones. This should be fixed in a next update.