@Pesky Rob - What percentage of your audience is on IOS? You can take a look at it by going to the Campaign Analytics and “Advanced Reports” to see your mix Phone/iPad audience percentages. If it’s a large percentage, it could be a contributing factor - but from what people are saying, the “inverse” should be happening (open rates for IOS to be 100% since their new anonymizing service “opens” all the emails). Since your CTR’s are down, this might not be an IOS specific issue. Here’s some helpful articles I found useful to navigate this by Klaviyo’s team:
Check to see if any specific inbox provider (e.g. Gmail) is a contributing to the lower open rates. If you see any one inbox provider drop relative to others, you might have a deliverability issue - in other words, your emails are going into Spam Folders in bulk.
I don’t want to make any presumptions, but have you been practicing good List management and sending practices? Here’s some more resources:
Hope this helps you find a path to a solution!