The error message you received is really not helpful, but indicates that your Popover component is being loaded dynamically using a Component Factory under the hood, but things are not resolving correctly. The Ionic 4 documentation (as of the time of this post) doesn’t explain that in order to get things working you’ll need to make the Angular Router aware of your component by adding it to the routing configuration.
So, for your component, you’ll want to add something like the following, e.g., for a lazy loaded route:
Once you do that, the easiest way to create your popup is to use a direct reference to the PopMenu component rather than a string format, so you’ll want to change your example above to something like: