How to fix strange colours on preview for MacOS Catalina

I have a late 2013 21.5" iMac and when I downloaded Shotcut onto it, there were strange colours on the preview screen. It was like there was a filter applied to it when there wasn’t. When the video exported, it was fine but it didn’t look right on the preview.

You can also see in the tiny thumbnail that the colours are normal and not altered.

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Maybe, but the old version listed also has problems.