PostgreSQL Upgrade (v9.5 to v12) with Django 2.0

Dear Community,

We are in the process of planning a PostgreSQL upgrade and would greatly appreciate any insights, best practices, or lessons learned from your experiences.

Current Setup:
   - PostgreSQL version: 9.5
   - Django version: 2.0
   - Database size: ~3 TB
   - One Master 4 Replicas(Streaming Replication)

We are taking a phased approach to this upgrade. In Phase 1, our goal is to upgrade PostgreSQL from v9.5 to v12, ensuring compatibility with our current Django 2.0 application.

As part of this, I would like to understand:

- What is the highest PostgreSQL version reliably supported with Django 2.0?
- What upgrade strategies or methods have worked well for you in similar environments?
- Any gotchas or performance considerations to keep in mind with large databases during such upgrades?

Your recommendations and experiences will be extremely valuable in helping us plan and execute this upgrade smoothly.

Thank you in advance for your support!