If you are unable to paste, then most likely it means the clipboard is still empty, which also means it didn't copy correctly.
I have used some applications in the past where the "copy" command was broken in a particular version of an app. It wasn't system wide.
Here's a test for you. Open "Notepad", type something, and try to Copy it. Space down a few lines and then try to paste it. If it pastes there, then the fault isn't with Windows 10, but whatever program you were trying to copy from.
Also, there are several 3rd party "Clipboard management" programs that start with Windows, and one of them may have been installed on your system prior to the upgrade. Some of these programs are not compatible with Windows 10 and will cause conflicts. I had one such issue with a mouse helper program I was using and a clipboard manager as well.
Some of the clipboard enhancement programs are installed with a new PC as well, but not very common.
May not be the case for you, but it's a possibility, so I thought I'd throw it out there and see if it sticks to the wall. (If you don't get that reference, you can throw spaghetti noodles and if they stick to the wall, they are done. Please don't try that at home, it's awful messy. Fun way to teach children to cook spaghetti, though.)