RT-BE88U - Any way to set Wi-fi 2,4 Ghz network into legacy mode (b/g/n)?

[Marsi4eg]

I'm currently using Merlin 3006.102.6 fw on my BE88U. That's annoying that wi-fi settings was separated to 2 different locations, and the new interface of basic settings lacks the "Wireless mode" setting that usually contained options like "auto", "bg only", "n only" etc. The problem is I can't connect an old device - PSP to the network, it just doesn't see it. It's probably because the network operates automatically in n+ax mode or something like that, while PSP is 802.11b device.

How can I enable legacy 2,4 modes with this "new" wi-fi network settings? Maybe there's an NVRAM parameter leftover that could be changed properly and commited?

Thanks