Thanks for coming back, matt17.
As we're not trained accountants or HMRC we can't tell you which codes to use. We can advise on which codes we have to select and what boxes they impact in Quickbooks VAT 100 report however.
For more information about the VAT codes and how they impact the boxes on the VAT return, see the Common VAT Codes article. This can help you decide on which code is correct for your products. Also, HMRC has guidelines regarding the codes, too. Check their VAT articles list for more details. We also publish the Brexit FAQ article regarding the Brexit event. Check it out if you want to get the details on the changes in QuickBooks Online after Brexit.
We'd recommend speaking with HMRC or an accountant if you're unsure which code to use.
I've got you covered if you have concerns regarding your products or transactions or any QuickBooks related. Just reply to this post and I'll get back to you. You have a good one.