Hi,

There are lot of changes in v13,

* Remove all the decorators @api.multi, @api.returns, @api.one, @api.cr, @api.model_cr from the code. Now they are all multi-record by default. In case of the last ones, you will need to adapt the code to the behavior change.

* Check that all "compute" methods of non-stored computed fields assign a value in any case to the field, even if it is a falsy one

* Computed stored fields will keep their previous value if not assigned during the compute method, so don't rely on any expected default value

* Replace sudo(user): "deprecated use of sudo(user), use with_user(user) instead

Like this there are many changes, you can checkout the below links and see,

1. Migration to version 13.0

2. 12.0- → 13.0

• Video: How To Migrate Odoo Modules To Another Version

Thanks