Jetpack’s Mobile Theme was deprecated in March, 2020.
Originally, we created the Mobile Theme feature as a fallback when the main theme on a site did not include responsive layout. Instead of showing a badly scaled desktop version of the site, it would display a very basic, text-focused layout.
Nearly every theme in use today includes a responsive layout for mobile devices by default now, so our Mobile Theme is no longer necessary.
It’s very likely that your current theme is already responsive. Your theme’s documentation will indicate this, but if you can’t find it there, you should reach out to your theme’s developers directly.
If you find that your theme is not responsive, we highly suggest finding a newer theme immediately since a huge amount of website traffic comes from mobile devices. If you have Jetpack, you can choose any one of the themes available in the WordPress.com Themes list. They are all mobile-friendly.
Responsive themes offer an easy way to set up a website that looks great on any device, whether it’s a desktop computer, laptop, tablet, or phone. In addition to loading properly on any screen, the best responsive themes are easier to navigate and are specifically coded for performance on these devices.