* "Israeli" is the proper adjective: It's the official and widely accepted term used to describe anything related to Israel, including its people, culture, language, etc.
* "Hebrew" refers to the language and ancient people: While the Hebrew language is spoken in Israel, it's not a defining characteristic of the modern nation. "Hebrew" is also associated with the ancient Israelites who lived in the land before the modern state of Israel was founded.
Therefore, "Israeli" is the correct and preferred adjective for Israel.
You can use "Hebrew" to refer to the language or the ancient people, but avoid using it to describe the modern nation or its citizens.