I have not tried doing that. I was not aware that was an option. Thank you for sharing. However, what do you mean by "set your read-only fields?" Do you mean set them from my views? I would like the field (not just the form) to be secure from unauthorized access.

I mean use the READONLY (or STATES) attribute at the field level.

According to the documentation, "this only has an impact on the UI." https://www.odoo.com/documentation/13.0/reference/orm.html#fields

Is there a way of securing the system in the database level (not just the form level).

The documentation is meaning to convey that users have no way to set values for these fields directly (even by importing) but the API can still be used to give them a value - programatically. Odoo users don't have direct access to PostgreSQL. You only have to control database level access for users YOU give access to the database. If you mean the Odoo business object level, then GROUPS (which can be assigned at the field level) provide what you ask. See the "FIELD ACCESS" section of https://www.odoo.com/documentation/13.0/reference/security.html

You said that "the API can still be used to give them a value - programatically." I thought anyone can access the API? Or do they have to be a PostgreSQL user?

Also, for the link you sent, the documentation says "attempts to (explicitly) read from or write to restricted fields results in an access error." I can't distinguish from read and write with the groups attribute. I need that distinction.