Don't use Lightroom Classic CC, which REQUIRES photos to be stored locally. Only use LR CC, and your photos will be stored only in the cloud.
The combination you want of using LR Classic CC with photos stored only in the cloud is not possible, unless you perform a lot of manual workarounds.
AND I DON’T WANT THIS.On LRCC I’ve unchecked « store original locally », but once I open the flow of the sync on LRC all my photos start being downloaded and imported.
How can I prevent this?
Unfortunately, that's how Lightroom Classic works. Once you enable sync in LR Classic there is no way to stop the images being synced from the cloud. In short, the workflow you would like to have is not supported.
So, in short, if you want to continue using Lightroom Classic CC without being encumbered with images from the cloud, then don't enable the sync feature.
Thank you all for your responses.
I will go and find other cloud for storage.