Error at deploying firestore rules - "This operation is not available for Cloud Firestore projects in Datastore Mode"

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Hello everyone. I am here for a few weeks. I am building an MVP app for my startup. However, there is a problem with firestore rules. When I try to deploy them, this error message pops out: "This operation is not available for Cloud Firestore projects in Datastore Mode."

P.S. I have set up authorization.

My question:

Why I get this error in a simple app? Which feature may I use that is not in Datastore mode? Maybe I can replace that thing with something supported in Datastore mode.

Generally how can I solve the error?

If the answer is switching to Native, this solution is problmatic because I should create new firebase project for that. However, I already set up the backend logic, so if I create new one, I should do all things again??

Thanks in advance, it will really help.

What have you tried so far?
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