Select the clips that need to be automatically adjusted on the timeline.
Click "Trim" > "Auto Adjust" in the menu bar.
In the Auto-adjustment dialog box, you can choose the auto-adjustment method. Usually, the Clip and Spacing option can be used to adjust clips and spacing to a new length.
Click the Apply button, and Final Cut Pro will automatically adjust the length of the selected clip to fit other footage on the timeline.
It should be noted that automatically adjusting the length of the clip may lead to a decline in the quality of video or audio, so it is recommended to check it when using this function and make manual adjustment as needed.