User475983607 posted
You did not provide any code, explained how the application works, or shared what version of Blazor you are using. If this is a WASM application then more than likely you need Web API or some other service running on a server to invoke CRUD operation
on a remote data store.
Can I also do the OOP(Interface and SqlRepository) on Blazor?
Yes. C# is an object oriented language. However, a repository pattern is often an antipattern. A better approach is a service pattern.
but I'm having this errors, specially when I'm putting a constructor in partial class, is this possible?
We cannot see your code and you did not provide the error. We can only guess what programming problems you are experiencing.