If that doesn’t work, check with your hosting provider if the have a security setting that may cause such an issue – for instance, they have the REST API disabled.
go to Appearance > GeneratePress then Right Click > Inspect the page to open the Browser developers tools.
Check the Console tab for any errors ( in red ).
Then click update
Ok, can so the REST API ( wp-json ) is not loading as the requests is being made to a HTTP URL.
Can you go to Dashboard > Settings > General and check that the 2 URLS there are HTTPS ?