Hi respected SIMONE MELIS,
Thanks for your valuable feedback and sharing updates with us and I really appreciate your effort and your precious time doing.
And I appreciate your kind words.
It sems that you want to keep some of Folder available on PC and while currently all your Folder/ files are online available.
As per your screenshot your Folder is mark as "Always keep on this device" have the green circle with the white check mark via right-click on Folder. These Folder download to your device and take up space, but they’re always there for you even when you’re offline.
The option "Always keep on this device" will help you to download this file/folder to your device. Normally, when you set up your OneDrive, all OneDrive files in the File Explorer (OneDrive sync folder) won't take up space on your computer. When you open one OneDrive file or select the option "Always keep on this device", the OneDrive app will download it. After that, you can open/edit these files offline.
Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Waqas Muhammad