Apple watch not able to unlock imac
I've just got an iPhone 15 and had trouble connecting my apple watch once i'd set the phone up. After a lot of trying to figure it out, I re-set the watch and paired it as a new one. But now it wont unlock my imac like it use to. To make matters worse, the 'allow apple watch to unlock' option is not showing in security & privacy. Anyone help?
2015 iMac running Catalina 10.15.7
Phone, watch and iMac are all showing as logged into iCloud and on the same account
iMac 21.5″, macOS 10.15