May I know where you have created the new users account, if you are trying to create a user from Entra ID there are two options to create a password one is manual way and Auto-generated Password. By default, when you create a user Auto-generated Password is selected while creating the account may be this might be the reason you don't get an option to enter a password.
If you have already created a user, you can reset the password for new password.
If you want to remove the device from Entra Join, you need to create a local admin account in your device and use the same credentials when you disconnect from Entra join.
Hope this helps. If you still do not see enough information to isolate the issue, please let me know the comment section.
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