There are values computed by the system that teams managing specific custom objects shouldn't be able to modify.

Example:

1- policy Number (generated following specific convention)

2- Dates that exist to track specific actions (ie: Policy got active, or cancelled, etc.)

3- There are multiple use cases where the system needs to generate a value, and people should not be able tto change those read-only values but others in the object.

A simple approach would be to have a custom field that act as a (just text), so when the system fill-out that custom field (that is just readable text), no one can change it out , except a system .

See attached image where I show a custom field which is a Policy Number, the support managing the policy shouldn not be able to change it at all, so instead a input field , it can be just a label text (as it looks on the red line value)