Please take a look at https://9to5google.com/2020/12/30/android-smart-selection-feature-now-lets-you-convert-to-other-units/.
On every android device, when you select some text that contains a currency (e.g. "300 EUR"), it will automatically suggest a special button called "convert". When you press it, you will be redirected to your default browser+search engine with the selected string and prefixed with "convert". (see the example in the linked URL).
This works fine for most of the units, searching for "convert 30 mph" will automatically give the expected value, but it doesn't work for currencies yet. Searching for "300 EUR" should give the conversion in the preferred currency.
Also see https://kagifeedback.org/d/3271-short-currency-conversion-queries-100-usd-should-default-to-regions-currency
