Facebook email links open in browser, not app
I had this issue and figured it out with no help for anywhere because it is fairly rare. The question was asked here some time ago, but it was closed and I was unable to reply.
Issue: Facebook sends you an email notification with a button/link to click. When you do, it opens Facebook in a browser rather than the app. It doesn't matter what email app is used. No info here nor on Facebook help/support.
My fix: I am using a Microsoft account (MSN, Hotmail, Outlook, etc.) with a 365 subscription.
*Open Outlook on a desktop using outlook.live.com.
*Go to settings/premium/security (below Features)/Turn off Advanced Security.
Previous to this change, Outlook changes all web links received through a Microsoft 365 subscription account into a link that is filtered through the Microsoft security system. The iPhone is unable to identify that it is a Facebook, or any other application link and will default to opening it in the default browser.
Note: Changing this setting will not update the links in any previously received emails.
iPhone 15 Pro Max