My apologies if I'm doing this wrong (new to github), but I made a pull request to update the CreateUser file. Let me know any issues...
#181

I couldn't recreate this in the latest dev branch.

php spark auth:create_user


CodeIgniter CLI Tool - Version 4.0.2 - Server-Time: 2020-04-07 09:15:47am

Username: test
Email: test@test.com
New user created: test, #2

Can you tell me what's happening with the password field in your scenario?
Since the field is required, how is the password being generated?
password_hash varchar(255) NOT NULL,

I just ran through a fresh install, following these steps below... same issue. I'm not discounting that this may be my fault in some way, but I don't see it yet. Please let me know if I'm missing something.

d:\xampp\htdocs>composer create-project codeigniter4/appstarter CI4 -s rc
d:\xampp\htdocs>cd CI4
d:\xampp\htdocs\CI4>composer config minimum-stability dev
d:\xampp\htdocs\CI4>composer require myth/auth
CI4\app\Config\App.php - public $baseURL = 'http://localhost/CI4/public/';
CI4\app\Config\Database.php - updated
d:\xampp\htdocs\CI4>php spark migrate -all
CodeIgniter CLI Tool - Version 4.0.2 - Server-Time: 2020-04-07 09:01:52am

Running all new migrations...
Running: (Tests\Support) 20160428212500_Tests\Support\Database\Migrations\Migration_Create_test_tables
Running: (Myth\Auth) 2017-11-20-223112_Myth\Auth\Database\Migrations\CreateAuthTables
Running: (Tests\Support) 2020-02-22-222222_Tests\Support\Database\Migrations\ExampleMigration
Done

d:\xampp\htdocs\CI4>php spark auth:publish

CodeIgniter CLI Tool - Version 4.0.2 - Server-Time: 2020-04-07 09:03:31am

Publish Migration? [y, n]: y
created: Database/Migrations/2017-11-20-223112_create_auth_tables.php
Remember to run spark migrate -all to migrate the database.
Publish Models? [y, n]: y
created: Models/LoginModel.php
created: Models/UserModel.php
Publish Entities? [y, n]: y
created: Entities/User.php
Publish Controller? [y, n]: y
created: Controllers/AuthController.php
Publish Views? [y, n]: y
created: Views/Auth/emails\activation.php
created: Views/Auth/emails\forgot.php
created: Views/Auth/forgot.php
created: Views/Auth/layout.php
created: Views/Auth/login.php
created: Views/Auth/register.php
created: Views/Auth/reset.php
created: Views/Auth/_footer.php
created: Views/Auth/_header.php
created: Views/Auth/_message_block.php
created: Views/Auth/_navbar.php
Publish Config file? [y, n]: y
created: Config/Auth.php
Publish Language file? [y, n]: y
created: Language/en/Auth.php

d:\xampp\htdocs\CI4>php spark auth:create_user

CodeIgniter CLI Tool - Version 4.0.2 - Server-Time: 2020-04-07 09:03:53am

Username: admin
Email: myemail@myhost.com
The password_hash field is required.

As I said, please use the latest dev version. In your composer.json file:

"myth/auth": "dev-develop"

I also strongly advise you not to use:

"minimum-stability": "dev"

...unless you're just checking out the project.

Well it's interesting to me that this worked... I'm new to composer/github, and I had assumed this would install the latest:
composer require myth/auth
I initially wasn't able to install auth without setting the minimum stability. I updated composer.json as you mentioned, removed the minimum stability, and used composer update to install.

Thanks for your help