Creating a budget is offered and available in the QBO Plus and Advanced versions, ProBrewer.
You might be using either the Simple Start or Essentials plan. This can be the reason why you can't see the Budget option. The list of available features based on the level of plan in this link: https://quickbooks.intuit.com/pricing/.
You can upgrade your subscription to be able to use this feature. Follow the steps in this article on how to do it: Upgrade your QuickBooks Online subscription.
Then, follow the steps here to create a budget: Create and import budgets into QuickBooks Online.
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