there is no implicit reference conversion from 'xxxx.Database.Domain.Entities.Order' to 'System.IDisposable'
Current definition requires TEntity (i.e. Person) to be disposable (you have put IDisposable to constraints of generic type)
public class UnitOfWork<TEntity> where TEntity : class, IDisposable
But I think you want object to be disposable, and entity to be of reference type. So, change definition to
public class UnitOfWork<TEntity> : IDisposable
where TEntity : class