with the remote in UART mode, if you don’t have the proper battery settings programmed in you won’t get an accurate reading but you should still get a reading.
AFAIK the only difference between the VESC4 and VESC6 variants of the VX2 is a 6p or 7p JST plug and the swapping of TX/RX.
Current Bidirectional is meant for things like eFoils and other prop control where “brake” isn’t really brake you need reverse to “brake”
have you gone into the remote settings on the VX2 it’s self and tried different ESC setting options? there shoul be one that cycles through “FSESC, FOCBOX and VESC” or something like that.