Monzo don’t charge fees for using your card abroad 
They will however charge a 3% rate on any ATM withdrawals after your £200 free limit (i.e. if you withdraw £200 worth of Euros it’ll be free but any ATM usage after that will cost you a little bit of money) 
Make sure you take a look at these guides before you go on your travels 
They’re super handy!
https://community.monzo.com/t/dynamic-currency-conversion-with-examples-guide-for-travellers/15919?u=nexusmaniac
https://community.monzo.com/t/monzo-in-france-discussion/9921?u=nexusmaniac
https://community.monzo.com/t/fr-monzo-in-france-wiki/3241?u=nexusmaniac