Open the QuickTime movie in QuickTime Player
Click File
Click Export As
Choose the desired resolution
Save the file with an .mp4 extension if available
If MP4 is not available, use File > Export As and select a compatible format, then convert it with another app
Open the video in iMovie or another video converter if needed
Choose Export or Share
Select MP4 or H.264 format
Save the exported file to your Mac
Use a third-party converter like HandBrake if QuickTime Player does not offer MP4 export
Open the converter app
Import the QuickTime movie
Select MP4 as the output format
Start the conversion
Save the converted MP4 file