If you are looking to remove the Starter Templates button visible on the top of the Pages/Posts of your website.
You can insert the following filter in your child theme’s functions.php file (How?) –
You can insert the following filter –
1) To disable the Gutenberg Templates button from all post types.
add_filter( 'ast_block_templates_disable', '__return_true' );
2) To disable the Gutenberg Templates button for Page post type.
add_filter( 'ast_block_templates_disable', function( $default = false ) { if( isset( $_REQUEST['post_type'] ) && 'page' === $_REQUEST['post_type'] ) { return true; } return $default; } );
Note:
Please add the required code to the functions.php of your child theme.
Refer to this doc on How to Add Custom Code to the Child theme?