Django Model field validation vs DRF Serializer field validation
Serializers are concerned with translating information to/from different formats for a model (text/json, etc.), and so the validation is in reference to this.
Model validation is a lower-level check, where the creation/modification of a db model is done. I always have model validation, even if I have serialization validation.
The field validation process can happen in 'Django Model level field declaration' or in 'Deserialization of data on DRF serialization section'. I have the following concerns regarding this validation process:

What is the separation of concerns? Which validation section should be placed where?
How the DRF serialization section restricts manual database entry with the validation?