You could create a new Cloud Firestore database,  where you can configure the database instance to run in Datastore mode which makes the database backwards-compatible with Cloud Datastore.
Cloud Firestore in Datastore mode uses Cloud Datastore system behavior but accesses Cloud Firestore's storage layer, removing the following Cloud Datastore limitations:
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Eventual consistency, all Cloud Datastore queries become strongly consistent.
 
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Transactions are no longer limited to 25 entity groups.
 
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Writes to an entity group are no longer limited to 1 per second.
 
Datastore mode disables Cloud Firestore features that are not compatible with Cloud Datastore:
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The project will accept Cloud Datastore API requests and deny Cloud Firestore API requests.
 
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The project will use Cloud Datastore indexes instead of Cloud Firestore indexes.
 
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You can use Cloud Datastore client libraries with this project but not Cloud Firestore client libraries.
 
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Cloud Firestore real-time capabilities will not be available.
 
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In the GCP Console, the database will use the Cloud Datastore viewer.