Hi there,
You could try something like this:
function isMobile() {
return preg_match("/(android|avantgo|blackberry|bolt|boost|cricket|docomo|fone|hiptop|mini|mobi|palm|phone|pie|tablet|up\.browser|up\.link|webos|wos)/i", $_SERVER["HTTP_USER_AGENT"]);
}
add_filter( 'option_generate_blog_settings', function( $options ) {
if ( isMobile() ) {
$options['infinite_scroll_button'] = true;
}
return $options;
} );
Adding PHP: https://docs.generatepress.com/article/adding-php/
This would assume the button is turned off in your settings (for desktop).