Install on RPI 4

you need to start reading what people actually write to you ...

But i am not able to access the web UI , so how can I make those changes!!!

try doing some more of this, including the links provided (seems this needs to be emphasized too)

OpenWrt Firmware Selector

is it okay to use the factory(ext4) version?
or should I use some other version

huh ?

you were already running openwrt, what are you doing now ?

or weren't you ?

No no, I am flashing it again, so I want to confirm is the factory version correct or not

I was using it , now flashing it again

why, and why not repeat the process from the last flash ?

I am doing it from the link u sent me , via wifi directly and no ethernet

well yes, but why the reflash ?

The WiFi is disabled by default and has to be enabled via the Raspbian OS. You have to set the Country Code for the WiFi there to enable it.
Have you done that already?

Yes I have activated the Wifi
i am getting an error in this command -
network.lan.ipaddr='192.168.2.1'

the error is - " network.lan.ipaddr='192.168.2.1' not found"

try reading that section again, you're almost there.

Yes now it is connected to wifi, what should I do next?

(re)read the thread from the 1st reply.

I have installed luci
but still not getting the web interface

firewall issue.

disable it, and it'll start to work.

/etc/init.d/firewall stop then
/etc/init.d/firewall disable