@Sherlock Might be a question to ask the manufacturer: https://support.oppo.com/en/?_ga=2.262621452.1882600921.1593027369-1276055379.1593027369
Is it not in display settings @Sherlock ?
I'm surprised you can't find it
I had this problem too, the blue light filter kept activating even with all the relevant settings double checked - I did manage to find a fix but it involves developer mode & changing settings via ADB so not the easiest fix!
I found it here: https://forum.xda-developers.com/showpost.php?p=75939435&postcount=6
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