You are using the new Apps Script IDE.
An IDE is more than just a code editor, it includes debugging, and other development tools that are not directly related to editing the code.
If you want, you can revert back to the "Legacy Editor" by clicking the blue link in the upper right hand corner.
It's possible to switch back and forth between "legacy" and new.
But to enable or remove an Advanced Service from your Apps Script project, you don't need to revert back to the legacy version.
The UI looks different, but the end result should be the same.
As a test, I just enabled Advanced Drive service in one of my Apps Script project using the new IDE,
and it now is listed under the "Services" heading in the left sidebar.
So, the option to add and remove Advanced Services is available in the new IDE.
There is no longer an OFF/ON button, but if the Advanced Service is listed, then it is ON.
The OFF/ON status button isn't really needed in the new IDE.
If you enabled an Advanced Service in the new IDE, then it's displayed in the list and it's active.