Ted here from Shopify, thanks for posting your query!
I'm trying to replicate this with the iPhone and Android version of the app but I'm not sure if we're seeing the same screen. At the moment I have the option to log into my account or I can create a new account, but both options are available. Here's a screenshot of what I can see:
If you're still not able to log in, could you share a screenshot of the error with me? What device are you using to access the app? In the meantime, you should be able to log into Shopify through your phone or tablets browser such as Chrome or Safari.
We do have another app called Shopify POS (iPhone and Android). If this is the app you're referencing please let me know. I don't believe there's an option to sign up for a new account as shown here but I'm happy to take a closer look into this with you.