Here are the steps which i will mention below that will let us use the full potential of GSI.
Ofcourse a working device
Installation Method :
First of all we need the flash the latest chinese beta rom.It gets updated everyweek. Since I have the cn rn7 i prefer to update the vendor partition everyweek for fixes and latest updates.But you can try on your stable rom too (I can't gurantee if things will work out on stable rom or not) .So, first of all be on china beta rom.
Go to fastboot mode and connect your pc to your device .You need to have installed xiaomi drivers to make this work properly. Once you are in fastboot ,open a terminal/cmd and type : fastboot -w ( this will erase your existing system partition and data and internal storage too , so make sure to have a backup if you have something essential on ur device)
Now considering that we have already downloaded a gsi i.e a phh GSI ..now for this case we are gonna assume its aosp as an example.. while in the fastboot mode type : fastboot flash system system.img ( here system.img(it can be of different name too) is the gsi img which you download from phh thread).
Remember : once the flash is completerd reboot to TWRP and not to system.
Once you are in twrp , flash magisk ( flash magisk latest canary as it has support for system as root devices) then press on wipe button of twrp,,,then advanced wipe..then tick mark on system and you will see repair or change file system option.Click on it..Click on repair and resize file system.
Now go to mount settings and mount system partition. Now you can flash gapps if you want .
After flashing gapps finally reboot to system
Voila! After in about 5 mins you will be booted to GSI rom
Post Installation Method :
You will have almost everything working after booting into gsi except you will run into brightness bug which you can fix by the following way
Connect your device with pc and enable mass storage
open a cmd/terminal on ur pc
type the following codes : adb shell
su ( in this case you will have to give permission from your device ; grant it)
setprop persist.sys.qcom-brightness 4095
Congragulations Now you have installed a gsi perfectly on your device
In this way you can flash almost all the gsi available on phh thread Hope this clarifies all of our problems.