I just want to follow up here for the benefit of others to share my final config.
It is possible to have two Inovelli Dimmers in a 3-way setup dim at both ends and keep everything in sync (on/off state and LED bar on both dimmers) with ZERO additional automations/hacks in HA.
I think the wiring setup I used is crucial.
- Master dimmer added to group 2 and group 4 of slave dimmer
- Slave dimmer added to group 3 of master dimmer
Stay sane!