It's not trivial to find it, you need to set it to dGPU only mode via mux switch and then let the LatencyMon test running for more than 120seconds.

(I'm not sure if it lags in igpu pass-through mode)

notebookcheck does report latencymon numbers and even remarks when it says the laptop is not recommended for real time audio:

https://www.notebookcheck.net/The-RTX-5090-Laptop-and-mini-L...

They don't see these extreme values though.