How can I use my Google Account with Apple apps (Mail, Calendar, etc) in OS X 10.10 and older?

For months, Google has been warning me that I "may lose access to apps that are using less secure sign-in technology". The warnings directed to [this page](https://support.google.com/accounts/answer/6010255) with more information. Starting on May 30, Google was planning to prevent software which does not use the modern OAuth2 authentication scheme from logging into any Google account. Unfortunately, this includes Apple applications built into OS X 10.10 and older, such as Mail, Contacts, and Calendar. (This applies even to accounts added via "Sign in with Google", and even though "less secure app access" was not previously required.) I am using OS X 10.9 Mavericks. As was foretold, on the morning of June 1, 2022 at around 7 am EDT, the Mail, Calendar, and Notes apps spontaneously became unable to connect to my Google account. How can I use my Google account without updating to an ugly flat version of OS X?