Hello @Seema_S, welcome to the UiPath community!
If you’re still encountering the issue, my guess is that you’re trying to access a cached / bookmarked site of the academy, particularly one of the courses. There has been some changes with the academy recently and some courses have now been retired, meaning that you will no longer be able to access them (via direct URL included). Which is probably why you’re getting the 404 error.
I would recommend that you access the academy via the following ways:
Also when logging in I would recommend that you log in using your email address and not just the username.
Hopefully this solves your issue, if not please feel free to reply so that we may try and help you out.
Happy learning, stay safe & healthy!