@Ed.Kok Yes, You can buy the C-variant with CAN and still use the USB-RS485 cable on the GPS-port (I think, it fits only in one port). I have this working with serialbattery.
I had a CAN-hat on my raspberry and got some action going on in Venus OS. I think from memory it said ERROR-ACTIVE...
You're not using the Multipluses to charge? Nice to see that You've been a good boy and got lots of goodies on x-mas :)
What software are You running on the ESP32?
I installed the newest 2.0x series of venus-os_dbus-seriabattery by mr-manuel and now the CAN-hat works really nice with my JK BMS. I ordered the CAN-version of my 4-8S BMS, and I can use te RS-485 adapter simultaneously.