What would be a good alternative to an Email for Account Creation

[Crazyroostereye]

So a Post I read recently here asking why Email is required for Registration made me think. Why is Email required. Everyone does it, but why actually do we need it and are there any alternatives?
So I thought about it and discovered 3 Aspects such an Alternative has to Achieve to be considered.

1. Reachability - to Reach the Person
2. Authenticate-ability - as an Alternative Auth, for example forgot Password.
3. Accessibility - It should be something everyone already has and can get.

The First 2 Obvious Ideas were Telephone and Address. These both fulfil all the Requirements. But they aren't better when considering Privacy as they are even harder to obscure or redirect. So I added Privacy as Concerned there.

Another One I remembered later is OAuth, something you most likely have seen in places already. This is when you use a different Party to authenticate. For example Google or Microsoft. But that suffers under the Issue of Accessibility as not everyone has an account with the Particular OAuth Provider the Admin chooses. And most OAuth providers resort back to Email. I wasn't able to think of any other Factor.

Does anyone here have any Idea?

[zonk]

I would amend your Accessibility criterion to be defined by a more important consideration: it's something everyone can have, whether or not they do already, without the approval of a third party. The important characteristic of email is not merely that it is well established and everyone is likely to already have one; it's the fact that email is completely decentralized and anyone with a computer can create a mailbox for themselves without having to create an account with any third party (if they know how).

Most people don't do this, because setting up a mail server from scratch is a huge pain, but it is possible, and even for those that don't know how, they still have the choice of providers, as opposed to, say, authenticating through Google, of which there is only one.

[Pearlple]

I think "Reachability" is the only real problem for the whole thing. Everything else can be solved.
(Email should always be an option for account creation.)

For example my current VPN provider is very privacy focused and allows account creation with just a username (maximum Accessability) and offers quite anonymous payments using Monero and such. (They used to allow cash via physical mail as well but it had too much administrative overhead for the number of users and might be illegal in some regions.)
Recoverability is obviously an issue here, but that can be solved in a similar way to your backup for 2FA methods. Just have a set of single use codes to recover your account. Of course you could lose those as well, but users who are so privacy conscious that they opt out of using email would usually be organized enough to keep such backup codes in a safe place, like a password vault or do some fancy cryptography stuff with it for fun. Otherwise they might just not care and accept they might lose this account. Alternatively this could be solved with an authenticator app or a physical security key/token. Each of them have advantages and drawbacks, but all have open standards and can be used in various ways, so letting users choose one or even multiple of these options should provide good accessibility and recoverability.

• email

• backup codes

• authenticator app

• security key

Then the only issue remaining is "Reachability". How this is handled depends on the reasons why it might be needed. If this is about ToS and the option to issue warnings for example, it could be solved by simply making users accept that if they do not provide their email, any breaking of the rules will lead to an immediate permanent ban.
I can't come up with any other reasons than that and recovery, why users might need to be reachable outside of the platform. Anything else (except maybe announcing a shutdown of the site) could be handled by a message on login.

[Crazyroostereye]

I would amend your Accessibility criterion to be defined by a more important consideration: it's something everyone can have, whether or not they do already, without the approval of a third party. The important characteristic of email is not merely that it is well established and everyone is likely to already have one; it's the fact that email is completely decentralized and anyone with a computer can create a mailbox for themselves without having to create an account with any third party (if they know how).

Yes I actually did add that to my Consideration but forgot to write it down, amended It, thank you.

My goal here is not to actually find an alternative. As I find Email is for this task the best. But I found it quite the Mind exercised thinking of systems that could replace email in that role. Another Idea I had been for example a Messaging Identity like Matrix or similar as they would provide the same Abilities except being less common. And therefore less Accessible.