Please, does someone know how to undo the desktop version?

Go to the top right corner and press the three lines, there you'll see a mobile version option click it and your done

I don't know if I'm just blind but I don't see any three lines on both sides

login first

beside the notification bell

Click on your pfp, it should be on the upper right of the page and there is a mobile version option there, mine works like that at least

Oh yeah since your have desktop version click the pfp on the top right corner there you'll see a mobile version option