Looks like this Item contains 2 Takes (also indicated by Take 1/2 in the Item header).
So select the first Take (with the Waveform) with your mouse and use Item > Take > Crop to active Take (also accessible via right-click on the Item: Take > ...).
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Make sure to check out the User Guide (
https://www.reaper.fm/userguide.php) and the Videos section (
https://www.reaper.fm/videos.php) in general.