Hello, @Schmitzlisan.

At this time, adding the account numbers on the printed checks isn't still available in QuickBooks Online (QBO). Yes, if you wish to add the account number when printing the checks, you can input it manually under the Memo field or add it to the vendor's profile.

On the other hand, you can also purchase or use pre-printed checks with the bank account number and routing number on it. You can check on the article provided by GarlynGay for more details: Order checks, tax forms, and other supplies.

I know how beneficial this feature for you and your business, I'll take note with this and pass along the information to our product engineers. This way, they may consider this feature in their future updates.

Let me know if you have any other questions. I'm always available to help!