Best way from CDG to Amboise without renting a car?

Take the train.

Indeed, take the train.

Either TGV to St Pierre des Corps and then backtrack to local to Amboise, or go into town (into Paris that is) and take the slow local train from Gare d'Austerlitz.

It's a bit of a walk into the central part of Amboise from the train station, but easily doable. I have done it several times.

thank you. we are really excited to go

Three options:

1. TGV from CDG to St Pierre des Corps, connect to Amboise by TER (regional train).
2. Go into Paris, take the TGV from Montparnasse to St Pierre des Corps, connect to Amboise by TER.
3. Go into Paris, take the regional train from Gare Austerlitz directly to Amboise, generally requires a train change at Orléans.
   

https://www.sncf-connect.com/
https://www.thetrainline.com/en-us

We chose the TGV to Tours route with the connection to Amboise when we went in 2022. But with the TGV train times and the unknown time factor of immigration lines, (very short vs very long connection time), we ended up with a long wait time in CDG that about killed us with jet lag - not many places to sit comfortably in the TGV station (or at least the good ones were taken at the time). I would personally pick next time to do the RER into Paris, then getting on the next slow train to Amboise to limit the down time in between. Keeping moving a little bit more before the longer train ride, and then one less stop. But that may not be everyone's preference.