If you are using Elementor Pro and are not able to create/edit the Elementor popup template. Try disabling the Header & Footer post types from Theme Settings > Custom Post Types > Post Types to fix this issue.

We recommend you create a custom header and footer using Elementor Pro. Because Elementor Pro has the custom Header & Footer functionality by default. If you are running Elementor Pro with Saasland, both custom Header & Footer functionality conflict with each other.

That’s why you can’t edit Elementor Pro templates, popups. You have to disable the theme’s custom Header & Footer to get the Elementor Pro templates working.