This is a mess imo! Before you had the OneDrive app and you had a OneDrive folder that you saw in File Explorer.
Now only the OneDrive folder is there and it only shows those files/folders that are available online and offline. While that is fine as far as it goes, if you need a file that you've got in a non-sync mode at your OneDrive web area, you have to use the browser to get to it at all.
That just isn't good at all imo and the only thing I think it will result in is less use of OneDrive for those things you want to keep but don't need instant access to. Or for those things that won't fit on your SSD equipped unit.
I'm not happy at all with this change and have provided feedback to MS about it.