The team is now working on the WordPress Interactivity API. This unblocks the same UX Frontity framework enabled but directly in WordPress Core, fully compatible with the new Site Editor.
Shortcodes in WordPress are just quick ways of generating HTML The result of the shortcodes is included in the rendered content available for posts via the REST API
Regarding Contact Form there are some updates pending to be done in the package (not maintained by the Frontity team) so that may lead to some issues. Have a look at the following post to learn more about this
Hope this helps
codemonkeynorth3
@mh123 see my comment here for a use-case (not for contact form but just in general)