Your question is a bit odd. There are two ways of using Turbotax, Online and Desktop. Desktop is the program installed on your Mac or PC from a CD or download. Online is online, and can be accessed from any computer with an up to date web browser. The iOS app is just a different portal to the Online version, there is no separate iOS app that runs on the device itself.
If you are unable to install the desktop version on your Windows 10 PC, you can create an account (or log into your regular account) with Turbotax Online and use any web browser on any Mac, PC or mobile device. If you buy the desktop version, there is a 60 day money back guarantee which will give you time to switch if you need to.
I don't know if the 4GB of RAM is a hard limit that will stop Turbotax from working, or is a guideline for best performance.
