Hi @tabibelkhirfaluc2, welcome to Thunkable! 
Be sure to check out our posts about How to ask Great Questions v2.0 and our Community Guidelines as you get started.
Sure, it is possible to use Google Sheets data instead of cloud variables for sending push notifications. We like Firebase because of it’s easy integration with Thunkable and its security but data is data and if you can access it properly, the call to OneSignal’s API will work the same.