I can't create a new mailbox on my iPhone

I’m trying to create a new mailbox, iCloud. iPhone 14, iOS 17.1.1…following this;

1. In the Mailboxes list, tap Edit in the upper-right corner, then tap New Mailbox.
2. Give your mailbox a name. If you have more than one email account set up on your device, tap Mailbox Location and choose the account where you want to create a mailbox.
3. Tap Save, then tap Done."

Easy enough, but it won’t work. Doesn’t show up.

Any other ideas?

[Re-Titled by Moderator]