Currently, OneDrive features making individual folders offline with one caveat:

"If you have multiple PCs, a file can be online-only on one PC and available offline on another. Any files you added to OneDrive from your PC or previously opened on your PC are automatically available offline on that PC. Any files you created on the OneDrive website or added to OneDrive from another device are online-only on your PC."

I wish there was the option to allow you to make a folder available offline and for it to auto sync files that were later added by another device later.

It's a bit of a hassle having to remember to uncheck and recheck "Make Available Offline" on a parent folder, because some files (which were added from another device) are online-only.