Ui template sensor file location

I have many template sensors created with the UI Template Sensor integration. The online documentation seems to indicate that this integration is no longer supported which is confusing.
Is there a way to add ‘class’ values to the sensors created via this integration? If so, where in the HA file structure are these sensor definitions located?
If this integration has indeed been abandoned, should I now be creating template sensors withing the body of the configuration.yaml file? It was my impression that yaml was slowly being removed from HA.

There is no such thing. There never was.

Template sensors have always been written in YAML.

Perhaps you are confusing templates with another type of integration?

If I’m not mistaken there was a custom integration for creating template sensors from the UI (see here) that you are probably referring to. But it has indeed been deprecated.

you will need to switch to using the built-in template sensor integration (via yaml) if you need to add things that the original custom integration doesn’t support.