@dghez, I’m going through the same process at the moment - the last theme I made was with Sage 8 and now I’m working on a new one with Sage 9. It’s a bit of a learning process with these new tools and the documentation is still not complete but with the forums, you should always be able to figure out what is needed.
All you need to do is upload the files in the theme folder. There’s no need to install Composer on your web server.
You can think of Composer as the PHP equivalent of Yarn - it manages and fetches the PHP dependencies and puts them in the
vendor folder. The files will be there once you have run
composer install (note: this will be done for you automatically if you set up your theme via the
composer create-project roots/sage your-theme-name dev-master command).
It can be confusing at first but once you’ve done it a few times, it makes a lot more sense
@JulienMelissas - DeployBot looks great but it might be overkill for this case (plus it costs at least $15/month). In the past I’ve used PHPloy with local Git repositories with good results. Or even simpler, I sometimes use Forklift to sync changes via SFTP.