Following on from Milestone https://github.com/rockstor/rockstor-core/milestone/20 we can now update our Django again to at least the next LTS, and ideally to 3.2 LTS. Depending on what our existing major dependencies allow.
Constrains:

• Django 2.2 LTS is compatible with Python versions: 3.5, 3.6, 3.7, 3.8 (added in 2.2.8), 3.9 (added in 2.2.17)
• Django 3.2 LTS is compatible with Python versions: 3.6, 3.7, 3.8, 3.9, 3.10 (added in 3.2.9)

https://docs.djangoproject.com/en/3.2/faq/install/
Our current testing channel, as of 5.0.0-0, uses Python 3.6.15 in all Leap targets (OS default) and Python 3.8.* in Tumbleweed.