Your question might be too general, as there is no silver bullet to make a model generalize.

My thoughts exactly… @Sylvain_Ard it may help for you to share a bit how the new data looks… just how different is it?
For me I take a very narrow starting point with object detection… and watch very carefully to see how the data changes (some call this data drift) … without knowing that it’s hard to say what you should do in the model… or in the data other than retrain your model(s)