Thank you for sharing the link to your site!
While looking at a 404 page, say this Link, can you hover on Elements in the admin bar and check if the Content Template is showing there?
Example: https://share.getcloudapp.com/KoujDnn6
If not, can you double check the Block Element you’ve created if the Element Type is correct or if the Location display is correct?
Perhaps you can also give us temporary access to your site so we can investigate further?
Please use the private information field for this: https://docs.generatepress.com/article/using-the-premium-support-forum/#private-information
Kindly let us know.