Why in the VAT 201 calculations report T3 and T4 show the same figure. Anyone know why this is please?

Thanks for dropping by, @accounts-alcomte. I can share some information about your VAT calculations report.
 
The setup of your sales tax determines how the system calculates VAT. 

Moreover, I’d also suggest consulting your accountant for guidance in reviewing your calculations report. 
 
How the amounts on the VAT report are calculated?
 

• The amounts on this report are calculates for the dates you choose at the top of the report screen.
• If you’ve backdated any transactions or made any changes to a transaction you have already filed (known as Exceptions), these will not be included on this screen.
• To see these transactions (known as Exceptions), refer to your VAT exception Report, or go to the Submit return screen. 
  
  

You can also check these articles for more details about:

VAT Detail Report.

Checking how much VAT you owe in QuickBooks Online.
 
If you have any trouble with any transactions in QuickBooks, please let me know and I’ll do everything I can to help here in the Community!