I just need a boolean to say whether the device is a desktop or not because the design team has given us requirements to behave differently depending on if the webpage is run on a desktop or a tablet. We can assume tablets mean iOS and Android, and desktop is Linux, Windows, MacOS. A Surface Pro would count as desktop. We cannot make any assumptions based on the screen size. There are large tablets and small desktops.
More broadly, we are using Expo React-Native (managed) web target, if CSS cannot provide this information.