Hide Form After a Successful Sign-Up
Hiding a form after it was successfully submitted is easy with HTML Forms.
Open up your form, navigate to the Settings tab and toggle the setting shown below to Yes.

This will hide your form fields after the form is submitted without errors. The success message you enter will still show, regardless of the setting.
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HTML Forms can store all of your form submissions in your database. You can then view these Submissions from inside the WordPress admin.
Roman Grigorian has written a great step-by-step guide on how to use the HTML Forms plugin with Google Tag Manager, Google Analytics, and Google Ads to track submissions: https://romangr.com/blog/gtm-html-forms