When I finish a job in a remote location, how can I create an invoice from a laptop without being able to connect to the internet?
This implies that you have cell service at the remote location. If so then you probably also have a phone with hotspot capability - which means as long as you have cell service you have internet.
Note that the mobile app is designed to work best with Simple Start and supports full features of simple start but not essentials, plus, advanced. There may be limitations on tasks you wish to perform when using the mobile app.
Here is a best of both worlds solution, if you need portability of a laptop but connectivity of a desktop - 4G (or new 5G) tablet instead of laptop. One with a nearly full version of Chrome browser available - such as a Surface Pro X