Use aistudio.google.com

Fyi anything on AIStudio can be used for training and/or review, do not upload anything sensitive there.

Not applicable if you are a paying customer. Only applicable to free plans.

https://ai.google.dev/gemini-api/terms#data-use-paid

For unpaid services there is no difference between aistudio vs gemini.google.com. They will harvest your data.

I like using Gemini without an API key.

You don’t need a key for aistudio.

I'm not sure what you mean. I use Gemini there and have never seen or created an API key.

https://aistudio.google.com/prompts/new_chat