The supported upgrade path is:
Upgrade from 3.x.x to 4.0.x
We recommend that you run the latest and greatest versions of Trellix ePO - On-prem, Trellix Agent, and Trellix DXL. See KB94079 for details about Trellix ePO - On-prem minimum supported extension versions. See the product documentation for Trellix DXL for details about upgrades.
Upgrade paths in a multi-TIE server environment
Given that you have different TIE server instances deployed in your environment, for example, a Primary, a Secondary, and a Reporting Secondary instance, perform a progressive upgrade.
Make sure the Secondary server database replication is up-to-date.
Upgrade the TIE extension
Always start with the Primary server, then continue with the other server instances you have.