please help me with some arguments for my wife

You're broadcasting to family who will likely be using gmail, so what difference does it make? Google will get all the emails either way. Anyway, logical argumentation is completely useless in a personal situation like that.

If you want the address to be stable in the long term, you should probably use your own domain name instead of gmail or proton, if you're not already doing that. After that, it's possible to switch the hosting without changing the email address.

A newborn doesn't need an email address

The problem isnt gmail, the problem is using an email for this purpose. Switching to protonmail wont make a difference. If you want privacy, use a different communications protocol. For example, use signal, and if anyone wants baby updates, they better install it too, cause thats the only way you'll send them.

Your daughter's Google account can be closed without appeal. All the memories gone. This less likely to happen using Proton or Tuta.

Id have been so pissed if my parents had destroyed any hope of privacy before i could tell them how fucked up that is. Your child didnt consent to letting google read about its life and see its pictures.

Whats her issue with using proton? It has all the features of google plus your setting ur kid up with a private ecosystem that will make them one of the very few who may have any hope of digital privacy in the future.

Could also just show her this comment chain where she can learn from us armchair experts.

https://www.theverge.com/2022/8/21/23315513/google-photos-csam-scanning-account-deletion-investigation

Google looks. Google reports. Even if you did nothing wrong you're guilty until you prove innocent and even then you'll never get your account back.

Well, unless you convert everyone else to proton or similar services, you're kinda screwed on the privacy end of things already. I mean, it's better than nothing, I guess, but it's you're sending to addresses that aren't privacy friendly, it's still exposed on the recipient's end.

Not worth arguing about on that level.

Now, if the account is actually going to be the kid's some day, that's different. You can make the point of making sure that their first account with an "all in one" provider be with a service that's a better "business neighbor" for all the associated services. Keep the Google account for the very few things that can't be avoided, but shift primary usage of email, password management, etc to the less obnoxious service provider because they're a better service rather than arguing about practically non existent privacy in email.

"arguments" alone don't suffice.

a demonstration of how easy it is to use proton drive (to share videos and millions of photos she's going to dump on relatives who are barely interested in seeing another baby photo) and protonMail would be more convincing.

Privacy interfaces have evolved to be attractive to lambda users.

when it comes to your wife uploading your daughters photographs to google servers, she can't decide alone: you share the authority (but would this argument matter in a marriage? No?

would having a protonMail matter if the photographs are attachments and recipients have gmail? No.

good luck. Not an easy task

Why not use the emails you guys already have? I don't think I or even you guys would want to use an email created by parents, since the username might not even be something they would have chosen for themselves.

Let them have an email when they are old enough to create their own. Use something like simplelogin maybe instead for an alias email instead that still comes to your email but looks separate for relatives it is sent to? I wouldn't want a premaid email account of my own before I was old enough.

I don't get the whole email thing, people are already doing that stuff on Facebook and your relatives are probably there too.

The offline photos idea would be a wise choice until the child has grown up and can make the decision but let us assume your wife will not accept that approach.

The Proton Drive idea also sounds reasonable since you already use that service. You should password protect the shared link but you will want another communication path than email to share the password to your shared folder. Use different folders with limited expiration dates (3 months?) for different sets of photos. Be sure to write to relatives that they are not to share the photos. We get emails asking us not to share things, be it links to photos or sensitive topics such as health. If someone breaks the rule, you may have to "ground" that person by cutting off their access to folder sharing for a period of time. You must communicate the "grounding" to others but that person might still go behind your back and get the link and password from a sympathetic someone else.

Have you thought about using a Fediverse instance for family and friends? There is a fantastic blog post on this subject. https://runyourown.social/ You would end up running a fork like Hometown that allows you to keep a portion of your community not federated where family and friends can share pictures with each other so that only users with accounts (plus your web server staff) can access your photos. https://github.com/hometown-fork/hometown You would be helping out many family members and friends instead of only helping your child. You would get more family and friends to support you because they would also be invested in making your Hometown server work for them. Find a relatively safe web server to host your data. https://www.eucloud.tech/en/eu-providers/vps-hosting