Basically Windows10 Update Error 0x800f0900 occurs when you are trying to update or upgrade using Windows Update and most probably due to some corrupt files on your system. So, if you're undergoing such issues then you may be able to communicate Windows support freely to urge cooperation. An accredited technician can assist you out. I'm sharing a link to at least one of these blogs, simply browse the online log and learn the procedure to work out this issue.

Blog: https://www.microsoftwindowssupportn...or-0x800f0900/