iPadOS: Double-tap window top shrinks it

I fully understand where you appear to be experiencing difficulties with your double-tap. This is one aspect of iPadOS 26 which can, until explained and understood, cause frustration.

A quick double-tap at the top of the a full-screen view will switch to windowed view as you observe. A quick double tap at the top of an App window does the reverse - switching to a full-screen view.

Insofar as returning to the top of a long page, you still use two taps at the top of the full-screen or active App window - but need to slow down...

Tap, briefly pause, then tap again; the page will scroll to the top exactly as you are accustomed.

Windowed Apps can be freely resized by dragging from any of the four corners of the window; this is signified by the "handle" icon at bottom-right of a resizable window. A tap of the multitasking control button (represented by the traffic-light button at top-left of an App window will expand the control; tapping red will close the App and associated App window, yellow will minimise the window but leave the App running in the background, while green will maximise the App window to a full screen view.

iPadOS 26 multitasking has received a significant makeover from that to which you may be accustomed in iPadOS 18.x and earlier - and may take a little time to learn and adjust your workflows. You would be well advised to review the official iPadOS User Guide and the many available online tutorials (such as YouTube) to become better acquainted with the new multitasking interface and associated gestures and controls.

Work with multiple windows at once on iPad - Apple Support

OS - iPadOS 26 - Apple

Multitask on iPad with iPadOS 26 - Apple Support (begin with the excellent inset video)

If you dislike the windowed environment, you can switch to using the basic Full-Screen App mode - but this disables all multitasking capabilities and hide the traffic-light controls; you will not be able to use split screen or slide-over modes with which you are likely familiar:

Settings > Multitasking & Gestures - select Full Screen Apps

director128 wrote:

Even when it’s set to full screen mode, there’s a bug where Stage Manager turns back on at some point while using a full-screen app.

I searched on Google, but unfortunately I couldn’t find anyone experiencing the same issue. The app causing the problem was a game.

I haven't encountered the problem that you describe - and have not seen any similar reports appearing here. If you have encountered a consistent or repeatable bug, you should submit a Bug Report via Apple's Product Feedback portal. For iPad and iPadOS:

Feedback - iPad - Apple

When submitting a report, be sure to include details of both the iPad model and installed version of iPadOS in the body of the report; do not rely upon the associated pick-list, as this is rarely up to date.

If your iPad is not operating as expected, try a forced-restart - as this will often clear an isolated software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

If the problem persists after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can perform the reset from iPad settings:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

If the problem still doesn’t clear, the next step is to reset the iPad to factory settings:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Otherwise, you might be well advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively and perhaps easier, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assist with troubleshooting:

Genius Bar Reservation and Apple Support Options - Apple

Even when it’s set to full screen mode, there’s a bug where Stage Manager turns back on at some point while using a full-screen app.

I searched on Google, but unfortunately I couldn’t find anyone experiencing the same issue. The app causing the problem was a game.

You're very welcome. I'm delighted to learn that you found the information helpful in resolving your difficulties.

While respecting your viewpoint, I sincerely recommend that you review the links provided - at least the short video that you'll find within the third link - as this will help you to get the best from your iPad.