My wife and I have had trouble for years with our Apple IDs/contact cards. It started when she was added to my T-Mobile phone plan. In the contacts app itself we only see our individual cards, however, when I update mine it will update hers as well sometimes, but not always.
Today we brought home a new MacBook from Costco and while setting it up with just her information the contacts app on the Mac showed my card as the default card and her contact card was also listed with her name but all her information was blank. We only signed in with her Apple ID, not mine.
Still on our phones we just see the individual cards associated with each phone. On the device list for each of our individual Apple IDs there is no overlap.
She gets my safari browsing history but I do not get hers. When I look up something on my phone she starts getting targeted ads and vice versa but we don’t get the ads for what we looked up on our own phones.
I’m at a loss, I feel like it’s either something with iCloud or our shared calendar or something T-Mobile somehow did. I’ve found numerous conversations here but did not find the exact scenario we’ve run into and while trying the recommended solutions still haven’t gotten a fix.