Edit: THANK YOU!!! Speedy answers - so helpful!!
Question has been asked for another date - but I’m in Paris and wanting to go to Giverny tomorrow (May 8). Am unable to get train times. Is this because train aren’t running or because I’m using the wrong tool (RATP app).
RATP is just for Paris and it's suburbs
You need to search the Normandy region train schedule here
https://www.ter.sncf.com/normandie
Vernon Giverny is the stop you want.
Another thing to keep in mind: May 8 (VE Day) is a national holiday in France and trains may be running weekend schedules.