Official notes are here: Victron Energy - Victron Professional
But it lacks detail.
The blog mentions it briefly:
Venus OS 3.50 now better handles Pylontech batteries experiencing cell voltage imbalance. For this improvement to be active, the GX needs to have access to the cell voltages from the Pylontech BMS. To check if a system has this capability, navigate to the Battery, then Details, and check for Lowest cell and Highest cell voltage readings. If not, it might indicate that the BMS doesn’t support it or needs a firmware update.
From Venus OS v3.50 - New User Interface, Security and Generator Improvements - Victron Energy
There is a beta topic that discusses the change in much more detail.