If I sign in with Apple and opt out of giving my email only to be faced with a prompt demanding I give up my email address, I'll be upset. I JUST told the app (via checking the box in Apple) that I don't want to give my mail, so why is it now suddenly required?
However if the app allows me to sign in and only asks for my email when I try to interact with a feature that would be more usable had I given my email, then I would be more accepting of it. Though I would still fully expect to be able to use the app in its entirety even if I opt out.
Now what Apple will say to this, I have no idea. But as a privacy conscious user, I would be happier with this.
As for having to come up with silly names, I don't understand why I need to be discoverable within an app. We have established social media and communication platforms, use them. Let me send a link to a friend to connect with them in your random app. I don't need to be able to add them within the dang app.
"Go find some setting and figure it out" is a UX fail. When I share eg a Dropbox link or a Google Photos link, you can get to it whether you have an established account or not. If there's something special about an app that requires an account before interaction is possible, then you can still make it a one-time share.
Yes, it does make user support more complicated. Yes, that's what I want and expect. I hope when I come asking for help, you can't help me because you have no clue who I am and have no way to get in touch with me because I used some email obscuring service. That's on me.
But in this case the company is someone who claims to be "The best way to create and share a grocery shopping list and organize your recipes."
Sharing is part of the deal with them and a sign in process that from the start complicates it is understandably a no go / introduces all sorts of complications that they detail in the article.
If the goal for the app is for itself to be a tool for identity management, then knowing my email is especially not needed...after all, all identity context is already in the app!
UX should center around ease of sharing some hash value across some other medium, not "searching by identity."
I do honestly empathize with the app creators. But anybody choosing an obscuring email by definition does not want to be identified by email.