I’ve installed the HolidayGoogle plugin, but it’s only showing one node: Holiday Google Controller.

The nodes for today and tomorrow aren’t listed.

Do you have any suggestions?

Have you setup authentication? Take a look at this topic https://forum.universal-devices.com/topic/43237-read-this-if-youre-unable-to-authenticate/

Yes, my authentication key only worked for 100 people. After that you need a complicated "review" process where you have to make a video, etc.

The only way is to create your own api key which you can enter as a parameter.