That's not possible. For example Mynymbox needs email addresses. It's up to you if you use a fake email or an alias or your real email. But it would be useful for you to rexdive emails for our invoices, service notifications etc.
We get sometimes tickets from our customer that they didn't know that an invoice was due and that their service is now suspendet. So ... 😀
"That's not possible" is odd to say in a reply to service that shows that something like it is very possible.
Mullvad also expires and it has to notify you about it, Mullvad also handles support tickets, etc.
Yes, you have some extra complexities, but not unsolvable.
Mullvad can do notifications because most of their users run the Mullvad VPN client. We don't have a client 😉
You highlighted one possible option: have a client. There are multiple things used on Tor that have a client, so that's possible.
I'm not saying these options are better, but I'm saying they are possible.
Asking users for email is the point of weakness - emails run on clearnet domains and if the email providers are kneeled on, they will provide the information to a three letter agency of your choice (e.g. proton did provide info in the past).
