Here's my take on this. It reflects my background, which includes 20 years in broadcast production and 10 years in IP telecom/video conferencing.

Surveillance cameras treat audio as an afterthought. It doesn't surprise me that they don't maintain sync sound. Most especially at the low end of the market. There's just not enough money in it, or motivation to get the details rights.

I prefer Grandstream cameras specifically because the company comes from a heritage of VoIP/Telecom. In telecom low-latency and sync sound area an absolute must.

They're multiprotocol capable. I can take the video stream via RTMP and the audio via SIP, which effectively a separate path using a soft phone on my vMix PC as the receive side.

Since I know SIP well I haven't bothered even trying to get the audio via the same stream as the video. I gather that this is possible since NVRs capture audio.