Mac mini M4 Quick Time Player stops recording

what location are you using as your "save to" location? I have, in the past, encountered issues with longer recordings stopping / not saving unexpectedly whenever I have selected anything other than "desktop" as my "save to" location. this has been especially true when "save to" is set to an external drive. so I now use "desktop" as my "save to" every time and afterwards I move them to my desired location manually. I haven't had an issue since.