Full screen mode: big images in landscape orientation are always shown at original size

Describe the bug
When using the full screen widget, landscape images larger than screen size are always displayed zoomed at original size. Only a portion of the image is visible, with (not working) scrollbars at side.
Portrait images are correctly shown (if screen is landscape, width > height).

To Reproduce
Steps to reproduce the behavior:

1. Open a landscape image.
2. Click on 'full screen' widget (square icon in the three dots menu)
3. The fulll screen mode is activated, but the image is not correctly resized to fit the screen.

Expected behavior
The image should fit screen size, being fully visible in its correct aspect ratio.

Screenshots
Image out of fullscreen

Same image in fullscreen mode:

Desktop (please complete the following information):

• OS: every tried: Android, Linux Mint, Ubuntu, Windows
• Browser: every tried: Fennec on mobile, Firefox, Brave, Librewolf

** Nextcloud version: **
v34.0.3 but this issue appeared several major versions ago.

Start by reproducing the problem in the full screen widget with a landscape image larger than the screen, then trace the image-sizing behavior used when fullscreen mode is activated. Compare it with the working portrait-image behavior. Done means oversized landscape images fit the screen fully while preserving their aspect ratio, without relying on non-working scrollbars.