Ha, it actually says that? Yeah having a dumb pop-up is pretty heavy handed. If there was a train as an alternative then I get it. The app seems to be under heavy development. When I first saw it it didn't have much outside of France, now it covers much of Europe... maybe you are outside of what is covered well.

Thats a little disingenuous that it only shows the CO2 impact of the cars.

https://ourworldindata.org/travel-carbon-footprint The above data doesnt consider manufacturing or infrastructure polution for the given mode of transport.