Recently I bought this board to play with wifi, but I cant build lvgl for it.

The PICO_W is supported on micropython master, but not in the lastest release, v1.9.1.

I tried few times to build lvgl and add then add PICO_W folder to the lv_micropython repo without success.

Can somebody with more experience guide me on thas task?

Just try to merge latest Micropython with the PICO_W support. There could be a few merge conflicts, but most are easy to fix.
What was the problem? What errors did you get?

I tried, but I really dont know what I did. Simply search on stackoverflow and copy some commands…but I simply move from one problems to another problems.

Normally add a new board is as easy as copy the board dir, but this PICO_W requires some changes on mpconfigboard.h and other files that makes it more difficult for me.

I will try again and let you know.
The errors I got, it was a very long errors cause there is somethign of lvlg missed on the compilation, so is not useful copy here.

What should be the required git commands to merge lv_micropython with the micropython master?

First add a micropython upstream remote:

git remote add micropython https://github.com/micropython/micropython.git
git fetch micropython

Then merge it

git merge micropython/master

Examine the output (or run git status) to see the conflicts and instruct git how to handle them.

I tried the commands you provide and manually merge few files, but finally got lot of errors on lv_mpy.c related with [-Werror=int-conversion] building the firmware.

Maybe micropython chaged a lot to merge with my few git skills. If merge is really a complex task I can try to use an ESP32 port for my projects for now an wait to the official LVGL upgrade.
I wanted PICO_W because it has wifi, but I really dont need PICO, so ESP32 can be good for me too.

That’s a good idea. ESP32 is supported well.
When a new official Micropython version is released, we’ll align lv_micropython to it.

Well then I’ll wait.
Also it is always good to practice with different platforms!