How to keep quicktime recording the screen while doing something else

I want to make a screen recording with quicktime, but I need to do other stuff at the same time, so I need to leave the recording "in the background" so to speak

I've tried starting a recording on one desktop and use another to work, the problem is that when I switch desktops, the recording area doesn't appear to move but it actually does and records whatever is on screen, it doesn't matter that I started the recording on one desktop and switched to another, it just records the one that is being displayed

I also tried starting a recording on one user account and fast switching to another, but when I switch accounts the recording stops

Another thing I wanted to try was using a second screen, the problem is that I have an iMac that doesn't have HDMI ports and I don't have converters or a second screen for that matter