Frequency? Do you mean Screen refresh rate or CPU Frequency?
If you mean Screen refresh rate. I think it's a normal behavior by MIUI rom that prevent thermal tempurature goes up too high. Because that, It will do anything to prevent that to happen such as trottle CPU Frequency, turn down screen brightness(Yes, still happen on MIUI13.0.3 if you play with high screen brightness) and most often "turn down screen refresh rate to 60hz". That's my guess, If I'm wrong please correct it up.
But network lag/stopping during gaming, I never face that issue. either Wifi and 4G.
I'm on Xiaomi.eu MIUI13.0.3 no root no modify anything else only install this 1.7.1-bat kernel.