How can my app show only the data of my users and not all data of all the users

You don’t need to do that manually, it can be done at the same time the users add their data.
There is a special value you can use - signed in users email address. Include a column to hold that in the table where they enter their data, and populate that as part of the Add Row action.

Then when you build a relation back to your User Profiles sheet (where you have Row Owners enabled), the data will be protected.

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