When you right click on the desktop or right click on an empty space in folders of nautilus you can select "paste".
Simply don't click on the three dot menu but below of this three dot menu on an empty space with a right-click.
I dont know if you're talking about pasting a file/folder, or if you're talking about pasting a directory/file path.
If you're talking about pasting a file or directory, just right click an empty space in the folder and select paste, or press CTRL+V.
If you're talking about pasting a path, its normal the button is gone, since Zorin OS 18 modified the way this works. Click into an empty space of the path bar (where it says Home / Desktop), doing that will switch into path editing mode (where you will see the actual path such as /home/yourname/Desktop/), then simply paste the path into this (since its now a text box once you're in edit mode, you can press CTRL+V or right click and press paste, but only once you're in edit mode), then press Enter.
So, You want something paste in this Direction Bar, yes? If yes, You can still do that. You go with Your Mouse Cursor in the Bar and click. Then the current Path is marked. And then make a Right-click and there You should have a Paste Option.
Not in the direction bar I usually press ctrl+L (lowercase) to edit the location. I am talking about the function that was present in the previous release.