If you have international transactions in your GBP account, this will automatically feed through into your VAT calculation, in GBP just like your other transactions. If you’ve supplied/purchased goods or services from outside the UK, then you may need to report some additional information to HMRC. The VAT calculation tool supports this type of cross border VAT reporting.
The VAT calculation tool doesn’t support non-GBP accounts, so the transactions in your Starling euro or US dollar business account aren’t included in transactions shown in the business toolkit. However, you can add these in as external transactions in the bookkeeping section, once you’ve applied the relevant HMRC foreign exchange rate to them.