I do not know of a solution to show a popup on a link, but dependent on your use case (especially the number of links and it's representation on the page) you may choose to hide the link with a macro. That is the user won't see the link (or anything that is inside) according to their permissions.
There are a couple of plugins you may choose from to get this functionality:
Hi my Community friends! For those who don't know me, I'm a product marketer on the Confluence Cloud team - nice to meet you! For those of you who do, you know that I've been all up in your Co...
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