It is there on English Wikipedia too, either on the sidebar or with that button if you hide it from the sidebar. However, it seems to not show up when you are logged out. Wikipedia often does not give as much customization options when logged out because they rely heavily on caching pages for logged out users to keep things fast
You can still change the width of the page by clicking the button in the bottom right of the screen
See
https://en.wikipedia.org/wiki/Wikipedia:Vector_2022
https://www.mediawiki.org/wiki/Reading/Web/Desktop_Improvements/Frequently_asked_questions