How to use my Surface slim pen to control powerpoint?

You configured Double-click = Open Microsoft PowerPoint, but you did NOT configure the button to control slides.

Opening PowerPoint is different from advancing slides.

In your screenshot I see:

“Pair pen” button is visible. That usually means the pen is NOT paired via Bluetooth — even if it writes.

Writing works without Bluetooth. The top button does NOT.

Settings → Bluetooth & Devices → Devices

Do you see:

Surface Slim Pen

If not:

Hold the top button for 5–7 seconds

The LED should blink

Add it as a Bluetooth device

Until this is done, the top button will do nothing.

Recommended setup for slide control:

Single-click → Nothing Double-click → Nothing Press and hold → Nothing

Then:

Turn ON

Allow apps to override the shortcut button behaviour

PowerPoint takes control automatically during Slide Show mode.

Open PowerPoint.

Start Slide Show (Press F5).

Now:

Single press of top button → Next slide

Press & hold → Previous slide