Subscriptions to QB

One QBO account is for one company file and you can use a QBO Accountant account to manage multi QBO accounts. If you need to manage multiple financial accounts and your clients don't need to access their data in real time, I would recommend to use QB Desktop Pro Plus or Premier Plus with a single user license.

Let me give you a warm welcome in the QuickBooks Community, @HPL2023. 

Like what 4Gal said, a QuickBooks Online Accountant (QBOA) account can handle managing multiple clients.

You can track multiple clients' financials directly by signing up to the ProAdvisor Preferred Pricing program and adding them to your QBOA account regardless of their QuickBooks Online (QBO) subscription status. Let me add further to this.

If your client already has a QBO subscription, you can ask them to invite you as their accountant user. However, if your client is new to QBO, you can either add the clients to their ProAdvisor Preferred Pricing plan and subscribe to QuickBooks for them or let them pay their subscription.

If your client doesn't have a QBO account yet, you can add them to your firm so all your client's information is in one place. 

You may refer to this article for further details about adding your clients' to your QBOA account: Add clients to QuickBooks Online Accountant.

I'm also adding this article as a future reference to keep track of your clients and update your client list: Manage clients in QuickBooks Online Accountant.

Should you have further questions about QuickBooks Online subscriptions, you're always welcome to leave us a reply. We'll do our best to assist you. Take care.