Neko Atsume Japanese Questions

[QuackingShoe]

https://jlptsensei.com/learn-japanese-grammar/じゃない-janai-ではない-dewa-nai-meaning/

https://jlptsensei.com/learn-japanese-grammar/けれども-keredo-mo-meaning/

Do you have a textbook or anything? ではない and such should be explained in any of them