When you connect a Google Sheet to Thunkable, every user of the app sends data to that same sheet. While you could connect a bunch of Google Sheets and code your app so that each new user gets connected to a different sheet, if you have more than a few users or you have an unknown number of users, you probably want to go with Firebase which allows you to dynamically create new user data on the fly rather than relying on an existing database structure as in a spreadsheet.
If you do look into Firebase, you’re going to want to use @drted’s method of saving & retrieving values using cloud variable path names: Replace GET or SAVE Blocks with cloud variables