I also have this issue with two identical ASUS PG27UCDM monitors running at 4K over a CalDigit Thunderbolt 5 dock via USB-C. Interestingly I can "trick" the OS into detecting the second display using BetterDisplay by loading and then unloading a custom EDID. When I load the custom EDID (generated using an online EDID creation tool), the main display turns off and the second turns on. After it's unloaded, both displays reset and work as normal. Would prefer to not have to buy an EDID passthrough emulator, haha.