A little late now, but you didn't have to uninstall 2018. You just had to sign in again, that's all. You can do that from either Photoshop or the CC desktop app.
It happens occasionally that the sign-in drops out. Nothing dramatic.
Adobe only supports current and previous version now, so 2021 and 2020 are those you will find available for download. But you should be able to find a 2018 download link here: https://prodesigntools.com/