The main takeway is that, now your theme source files should be located in a keycloak-theme directory somewhere in your src directory OR at the root of your directory.
Acceptable directory strucuture:
You don't need to have all three variant of the theme. If you only need the login theme for example you can have only the login directory.
If you had akeycloak_email_theme at the root of your project it must be move alongside the login/ and account/ directory.