Strange Popup Ad on my WordPress Admin Dashboard

It seems like a malware activity.

To find who is generating that pop-up you can deactivate all other plugins, revert to a default theme like TwentySeventeeen and test again. Then, simply activate them back one-by-one checking each time the installation process until you get the pop up again.

The plugin you mentioned shouldn’t be the problem since it’s not active.

You can also scan your site with this site to confirm.