I use the same Intel N-6235AC Wifi+BT card on my E6440 with OpenCore 0.6.7 Bootloader and Big Sur
I followed Dortania Guide and just installed 3 kexts, added their entries to config.plist and WiFi and BT are working fine:
AirportItlwm, IntelBluetoothFirmware, IntelBluetoothInjector
https://dortania.github.io/OpenCore-Install-Guide/ktext.html#wifi-and-bluetooth