Hey there!
The open filters in your segment are great to have but like you mentioned with the Apple Opens that can sometimes be a tad inflated.
Typically for my Engaged segment, I’ll filter in OR conditions for their purchase history, browse, checkout, active on site - anything that hints at that user being ‘engaged’ with the brand plus the OR condition of if they have email opens/clicks.
You could start at a small window for that - last 30 days then duplicate it, then changing it to 90, etc. So then you’ll have layers of engagement to test and send to. If you are worried about engagement levels, you can stick to emailing that smaller window and work your way up to the larger segments.