There are a bunch of cheap IP cameras (TP link IPCXXXX) by TP link that are sold in China:
https://www.tp-link.com.cn/list_2549.html

They use RTSP for video and audio streaming by default, and go2rtc picks up that without any issue.

But for two way talk, they have some proprietary protocols similar to that used in TAPO cameras, only difference is that it is wrapped inside RTSP instead of HTTP. Someone did a bit of packet capture and reverse engineering, and claimed that it was a RTSP MULTITRANS plugin. (https://iovxw.net/p/frigate/)

If anyone is interested in implementing it, I can provide a camera access for you, because I don't know how to do it.

Thank you!