All clusters will need to be upgraded at a point. If you have metro availability enabled in your environment, you will need to follow the best practices guide lines for it:
Specifically Nutanix supports the following replications:
- Between N to N-2 major versions and vice versa for STS to STS versions or LTS to STS versions.
- Between N to N-1 major versions and vice versa for LTS to LTS versions.