this is exactly the problem i've mentioned.
go to special page like last edited page and you'll find out
or also try to lock the right side bar instead of hiding and you will find out that the alignment is not the same
logged:

In T377653#10244090, @Aklapper wrote:

the left space is not aligned, it doesn't disappear well

Cannot reproduce. Firefox 130:

Other information (browser name/version, screenshots, etc.):

Please always include screenshots of visual problems, and please also try in safemode. Thanks!

ps: already already tried in safe mode (also in the screenshots)

the problem is that imho it doesn't make sense, at least it should be the same for every special pages (and not only for the ns0).
the other strange thing is that by showing the panel on the right, the spacing is reduced without being aligned and not uniformly...

https://it.wikipedia.org/wiki/File:Vector_2022_video-en.webm
jump at time: 00:46
as you can clearly see, the page aligns completely to the left.

it is not actually like that, i just checked again also on enwiki:

moreover, normal pages has the "vector-sticky-header" and some special pages (such as RecentChanges) don't. so when i scroll down everything disappear at the top... why these differences

as you can clearly see, the page aligns completely to the left.

Does this explain this behaviour?

In T377653#10342179, @GiovanniPen wrote:

moreover, normal pages has the "vector-sticky-header" and some special pages (such as RecentChanges) don't. so when i scroll down everything disappear at the top... why these differences

The sticky header only appears in certain namespace. The menu varies based on pages and T329673 tracks enabling it in different places.