Hi @Melaku.
Currently, the ability to generate and upload a budget in QuickBooks Online using Spreadsheet Sync is available only in the US region's QuickBooks Online (QBO) Advanced. It might be available in the QuickBooks Online UK version soon, or it may not.
In the meantime, you can consider checking the Apps menu to search for alternative applications that enables you to generate and upload budgets in QuickBooks Online.
For more details about Spreadsheet Sync and QBO integration, please see this article: Get started with Spreadsheet Sync for QuickBooks Online Advanced.
Additionally, this article may come in handy: Manage billing, payment, and subscription info in QuickBooks Online. It covers how to update your billing info and upgrade your subscription.
Please let me know if you need more QuickBooks Online assistance. I'm always here o help out more. Take care and stay healthy.