How to get red, yellow, and green buttons on iPad?

Enable windowed apps and you’ll see those buttons:

Turn Windowed Apps on or off on your iPad - Apple Support

The three dot button to control multitasking is still present - but is visually now a traffic-light button. The button location has changed. Instead of being top-centre of the App window (a location which frequently conflicted with controls for many third-party Apps - of which regular complaint was seen here), the button is now at top-left of App windows that are not being viewed in full screen mode.

For iPadOS 26, you have a configuration choice to use Full Screen Apps only, use Windowed Apps, or Stage Manager mode as you prefer. Selecting Full Screen Apps Only will completely disable the Windowed Apps mode - and with it, will remove the traffic-light (red, green and yellow) buttons from the left-hand corner of App Windows.

Settings > Multitasking & Gestures - select your preferred multitasking mode

The traffic-light button is used to control the App windows. For Apps that are being viewed in full screen mode, a simple downward swipe from the top-edge of the screen reveals the new menu bar - where the button is located at the left.

In more detail, iPadOS 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

Split View and Slide Over views remain - although are now accessed differently. You can have two or three App windows side-by-side - or a spit the screen into four quadrants.

To access, assuming that the current App window is not maximised; touch-and-hold the traffic-light icon at top-left of the App window to expose the Fill & Arrange options:

The current App window will move aside, allowing you to open another App; the selected view will open the selected Apps in their own windows - which can be resized laterally, as before, by dragging the divider to left or right.

If the App window is already maximised, swipe downwards from the top-edge of the screen to expose the new menu bar - then use the traffic-light icon as described above.