For first question:
The i2c is used to control the ET6326 to realize the breathing function of the led. which is implemented in /usr/bin/gl_i2c_led and you can refer to this link to learn about its implementation.
For second question:
I think you need to modify the driver to implement it, or you can refer to this patch? I think you should also encounter other difficulties, if you realize, I hope you can share with me.
https://github.com/gl-inet/gl-infra-builder/blob/main/patches-mt798x-7.6.6.1/3008-support-uart1-no-use-cts-and-rts.patch