The functionality to maintain VAT exchange rates currently only exists for Poland, Hungary and the Czech Republic localisations (Although being under the "EUROPE" localization in the microsoft documentation. This is a requirement in the UK also where HMRC expects UK VAT charged in a foreign currency to be posted based on the rate published by HMRC or a local rate (which can be different to the accounting exchange rate)

https://www.gov.uk/guidance/foreign-currency-transactions-vat-and-tour-operators

Furthermore, when a supplier invoice UK businesses with VAT in foreign currency, they specify the rate applicable on their invoice and it is common to apply this rate of for the VAT amount so the VAT reclaimed equals the VAT they paid. Amending the rate on the invoice as a whole is not a feasible solution as this also applies to the value of the goods which may distort inventory values or P&L cost