iPhone / iOS
iPhone (iOS) — After ClipKeep finishes extraction, tap the download option, then use the Share sheet to choose Save to Files or Save Video. Safari usually gives the most reliable save dialog on iPhone.
Android
Android — Chrome normally saves the MP4 directly to Downloads. If the video opens in a new tab, open the browser menu and choose Download or Save video.
Find the saved file
If you cannot find the file, check Files > Downloads on Android or the Files app on iPhone. Large HD videos may take a few seconds to appear after the browser finishes downloading.