Is this account an administrator

Let's verify whether your account has administrator access in QuickBooks Online, Xiao.

Here's a sample screenshot for visual reference. 

If you don't see the Manage Users option and the list of users, including their roles, we can confirm that you don't have administrator access.

In that case, I recommend reaching out to your primary or company admin so they can grant you the necessary permissions or update your role. This process will ensure you can create sub-accounts.

If you can access the Manage Users list and see that you are the primary or company admin, I suggest logging out and then logging back in to refresh the system.

Afterward, please create a sub-account in the Chart of Accounts once again.

Please let us know if you have further questions. We're always here to help.