I prefer style 2

Style 2 is better

All styles are good for me.

I like style 2

Style 3, is simple to find and read the documents.

I prefer Style 2
It looks more neat than style 1 and not overwhelming than style 3

For me, Style 2 works better because it separates navigation from on-page scanning, instead of forcing one sidebar to do both jobs.

A few reasons why this layout is stronger:

1. Left sidebar stays shallow and stable — capping it at 3 levels keeps the tree readable and predictable. Users always know where they are in the doc hierarchy without endless nested expansion.
2. Right-hand Page Directory handles the long tail — finer H2/H3-level headings
3. Reduces cognitive load — a single sidebar trying to show both document structure and in-page anchors gets cluttered fast, especially for long manual pages. Splitting them means each panel has one clear job.
4. Scales better for technical docs — as more upgrade guides, release notes, and best-practice pages get added, the left tree won't balloon into a 6-level nested mess. Page-specific detail is isolated to the right panel per page.
5. Faster scanning for returning users — someone who's read this page before can jump straight to "Pre-Upgrade Check" via the right nav without re-navigating the left tree.

Style 3; This allows direct access to specific information, saving time spent searching through the document.

I prefer Style 2

I like style 1.
style 1 provides a clean, focuses reading experience by limiting the left sidebar to 2 levels and offloading deeper headings to the right directory.