I am PV only and off grid so can't answer you on grid queries.
The ports that work with the Windows App are two marked RS485-2, these are the greyed out Uart-2 in the app that are fixed to JK-BMS RJ45 Modbus V1.0. So one can be used to connect to PC and 2nd to next battery.
To drop your charge voltage use the app to change the RCV from 3.45V to your preferred lower V 3.35V, I can leave mine at 55.2V as using PV it takes until 3 or 4pm before I get there and then the sun intensity drops so the voltage drops naturally. The float function volts settimgs in the BMS does not get to the SI so until that is fixed you need to change the RCV using the app.
I have an HiFlying Elfin EW11 connected to the RS485 port on the BMS to send the data to my Wifi and then use a virtual serial port on my PC 25 yds away to connect to the JK so I can change settings in comfort.
I am on Firmware 15.17, if further updates come that break functionality you can force a firmware upgrade to an earlier working firmware but you need an added code which you get from here.
https://mirofromdiro.github.io/JK-firmware-code/