Hello,
when you travel with SNCF TGV, there is no maximum luggage allowance, but you have to carry your luggages by yourself. You have a small space over your seat to put a small luggage and a jacket, and larger luggage spaces near the doors and near some seats for biggest luggages.
If you need some advice on how to store your luggages, you can ask the SNCF staff in the train.
For more information : https://www.sncf.com/sncv1/en/services/luggage
Regards.