The error message is telling you that your
Example.Model.Category
class needs to implement
Abp.Domain.Entities.IEntity<int>
if you want to use it as the generic type parameter in your
IRepository<TEntity>
interface.
Your interface has a constraint on its type parameter - something similar to:
interface IRepository<TEntity> where TEntity : IEntity<int>
Constraints on type parameters - C# Programming Guide | Microsoft Docs[
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