Can’t get offline mode to work on Sims 4

@a9c548c484f1d272cf67def3ad837362  If you login on another computer, do the email address and password you're using on the first computer work?  Have you changed your password since the last time you were online on your main computer, and if so, does the old password work?

Origin normally accepts the offline sign-in method you've described, but if the login data it's stored doesn't match what you're inputting, that would explain the issue.  It's also possible that the login data has been deleted, especially if you've cleared Origin's cache or use a tool that clears temp files.

By the way, a USB network adapter can cost $10-15 U.S.  I realize that the better solution would be able to play offline, but if Origin isn't going to cooperate, that's a valid workaround.  You might only need to login to Origin once before being able to use it in offline mode again, which means you could borrow an adapter from a friend or perhaps even use one at a computer repair shop instead of buying one outright.