I see the GL-AR300M and the GL-M9531 module is using the same CPU.
I can see the max tx power for the GL-M9531 is set to 29dBm and that the GL-AR300M is only 20dBm.
Will it be possible to increase the tx power on the GL-AR300M above 20dBm?
No. GL-M9531 is a module with signal amplifier but GL-AR300M router doesn’t have signal amplifier