Here is what wordpress.com wrote: Hi there!
Unfortunately, you can not disable Jetpack. That is what connects you to the WordPress.com platform. You can try disabling AMP in your settings. Other than that, you may want to consider using a theme that is more suitable for WordPress.com.
Please note that third-party themes may not be supported and we cannot always ensure compatibility with these as there are far too many for us to test them all.
Everything else concerning the PHP version is OK. We use the latest PHP versions (PHP 7+). You may want to consider exploring our selection of themes here on WordPress.com that are curated and vetted