The Classic Editor has been permanently deprecated. The WordPress Editor (i.e. the block editor) is the default editor in the Jetpack app. To learn more about the WordPress Editor, take a look at this guide:
As the Classic Editor is no longer being maintained, we strongly recommend using the WordPress Editor, so you can benefit from continued updates and improvements. If this isn’t an option, the Classic Block offers a very similar editing experience to the older editor. From a web browser, you can add the Classic Block to your post or page. Details on how to do this can be found here:
If your post only has Classic blocks, then you’ll be able to edit them through the app after they’ve been added via a browser. If not, you can edit a Classic block by tapping the question mark (?) on the respective block. Then you’ll see the “Edit using web editor” option and it will open an in-app browser that will allow you to edit the block.