This add-on automatically extends the timeline while animation playback is running.

It is shown as a tab in the Sidebar of the 3D Viewport (the N panel). Made & tested with Blender 4.3.

Click on the "Start Recording" button in the add-on panel to have the animation play. When the current frame is close to the end frame, the add-on will automatically push the end frame forward.

When you're done, simply press ESC or click again on the button: the playback stops, the final frame is set, and your timeline is trimmed exactly where it needs to be.

I'm going to publish a videotutorial on my youtube channel on May 30th (2025), so subscribe to my channel and turn on the notifications! ;)