Steps to replicate the issue (include links if applicable):

• Enable "Use the wikitext mode inside the visual editor" at https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-editing
• Use Google Chrome logged in.
• Edit a page filling more than a screen, e.g. https://en.wikipedia.org/w/index.php?title=Wikipedia:Sandbox&oldid=1250853473
• Make any change and click "Publish changes".
• Click "Show preview" in the popup.

What happens?:
A non-scrollable vertical bar is now displayed at the right. It covers the right side of the "Publish changes" button. Chrome screenshot:

What should have happened instead?:
In Firefox there are two vertical bars to the right. The rigthmost is not scrollable and is fully to the right of the "Publish changes" button. The leftmost bar is below the "Publish changes" button and is scrollable. Firefox screenshot:

Both screenshots were made in Vector 2022.

The non-scrollable bar appears to be made by this:

html.oo-ui-windowManager-modal-active:not(.oo-ui-windowManager-modal-active-fullscreen){
  scrollbar-gutter:stable
}

The bar should either be removed or displayed to the right of the scrollable bar.

Overriding the above with this personal CSS will remove the non-scrollable bar and make a working scroll bar visible behind it in Chrome:

html.oo-ui-windowManager-modal-active:not(.oo-ui-windowManager-modal-active-fullscreen) {
  scrollbar-gutter: auto !important;
}