Hi @MathiasGijsels,
If the data source for the Table is Dataverse for Teams, unfortunately the security configuration does not allow you to restrict data between Team Members. Team Members have access to all data. Only Guests added to the Team from outside the Tenant will be restricted to see data they create.
More information about Dataverse for Teams security here.
To achieve your scenario, you would need to use a full Dataverse database, which would require those using it to have a Power Apps per user or per app plan. Or you would need to look at using a SharePoint List and setup item level permissions so that users can only see their own items.
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