For some reason the app is showing multiple VAT rates simultaneously, also if I add another item in the app my standard VAT rate is not an option.

Hi there, @userdamion.

Welcome to the Community. QuickBooks Online is available to many countries around the globe. Each has region-specific features based on the mandates set by the government or tax agencies. 

In your case, I'd recommend uninstalling the app and ensure you choose your country upon reinstalling it so your standard rate would appear.  

Just in case, here's an article that you can read through: Setting up QuickBooks for GST. It helps you learn about adding GST in QuickBooks Online.

Feel free to message again if you have additional concerns. We're always here to help.