How to reproduce

1. Use a new setup of txs (i.e. remove files in config folder). Open a document with several pages and open the pdf in the windowed (internal) pdf-viewer. By Default options continuous and fit to width are set and the viewer shows a scrollbar and its slider allows scrolling through all pages. Narrow down the width of the viewer such that at least a full page fits the window (for me this is already the case). Uncheck continuous in the View menu.
2. Be aware that now any scrolling is used if a single page doesn't fit the height of the viewer to adjust the pages position (even so we could need one more to scroll through the pages as with continuous mode, but I think we can't have both). Please observe that the scrollbar is still present but the slider is missing. It is correct that there is no slider (and thus no scrollbar is needed at all) since we can see a full page (s. 1.).
3. If we would check continuous option again we would end up as at the beginning. But instead press button fit to window. The scrollbar disappears as we would expect. But now check continuous and see that the scrollbar is missing. If you press fit to width the scrollbar appears again (with slider). Now you can repeat this (uncheck continuous, slider is missing, ...).

If you would use fit to page in 1. then use fit to width then fit to page again in 3. to reproduce.

Environment

• TeXstudio: 4.2.3 and releases after that
• Qt: 6
• OS: Windows 10
• TeX distribution: miktex

Expected behavior

scrollbar should be present with slider, otherwise no scrollbar is needed. If a scrollbar is needed it should be present.