Can I use the LWM2M communication on BC68 with general IoT platforms (other than Huawei’s IoT platform)?
That depends on your expectations.
Generally it works also with the eclipse open source project leshan, you may test that with Leshan Sandbox.
Using plain coap (without encryption using DTLS), it works, but I would not consider to use that in the internet for production.
Using coaps (with encryption using DTLS) also works, but depending on your provider, your IP-address may change more frequently and that requires frequently handshakes (the BC68 offers a timeout for that).
Leshan uses Eclipse Californium, which offers a implementation of DTLS 1.2 - Connection ID to overcome that similar to Huawei’s DTLS+. But that would require some work from the firmware developers.
Regardless of coap or coaps, you may need to implement the a resource, which maps to the one the BC68 offers you as a generic way to communicate. I haven’t seen a way to add LWM2M resources on the BC68 side.