Google Ads is testing a way for advertisers to preview the impact of a change, like adding negative keywords. It seems to be called "Preview impact estimates" and lets you estimate the impact of, in this case, adding specific negative keywords.
This was spotted by Menachem Ani who shared a screenshot on X and wrote, "This is cool! Preview the impact of your negative keywords in Google."
Here is the screenshot:
As you can see, it says, "You can now view the impact of your negative keywords. Click the "Preview impact" button to view impact of up to 10 negative keywords."
I am not sure if this is fully rolled out to all advertisers or not.