One or more elements cannot be resolved during compilation because the element is not defined by the HTML spec, or there is no component or directive with such element selector.
This is the compiler equivalent of a common runtime error NG0304: '${tagName}' is not a known element: ….
Use the element name in the error to find the file(s) where the element is being used.
Check that the name and selector are correct. If the component is from a different module or import, check that the component is exported from its origin module and imported into the correct *.modules.ts file, and declared in the imports list.
When using custom elements or web components, ensure that you add CUSTOM_ELEMENTS_SCHEMAto the app module.
If this does not resolve the error, check the imported libraries for any recent changes to the exports and properties you are using, and restart your server.
