Hi, @bolaurent. Welcome to our Netlify community site.
There is a --baseurl command line flag which I think (I’m not a Jekyll expert) works the same way. I found this flag in the documentation here:
So, I believe a build command below might work for deploy previews (in netlify.toml):
[context.deploy-preview]
command = "jekyll build --baseurl $DEPLOY_PRIME_URL"
Would you be willing to please test that and let us know if it solves this issue?