Around 6 months ago, I made a OD share with my colleague from the same organization.
He was able to sync this share on his machine with the local OneDrive client.
My colleague had a breake for 6 months, during this time he was not working on that share.
Today he starts again with the work. We realized that it's not possible anymore, to sync the shared folder (where Im the owner of the share) with his local OneDrive Client. Accessing to the share over web is no problem.
Why is that so? Is there a workaround? If not, this fact would make the cooperation work over OneDrive really useless.
The article you referenced is about OneDrive consumer, so it does not apply to OneDrive for Business.
Your colleague should indeed be able to sync with the OneDrive client (NGSC) any folder you share with him. He should go, on the web UI, to the "Shared with Me" view, click on the shared folder, and then click on Sync in the action bar.