[Kerbal Space Program] I had a Kerbal Account but now I cannot access it, it takes me to a Private Division Account page

As of August 31, 2021, your KSP Account has been migrated to a Private Division Account. Your previous purchases are all available from within this new account, and to access them you must visit the Private Division Account portal, enter the email address you used to purchase KSP or create a KSP account with, and follow the upgrade instructions within.