The problem is that you are using the wrong field 🙂 That field is for excluding categories from results, when categories are the results – not the posts related to them.
To exclude the posts connected to the categories go to the Advanced Options panel and scroll down a bit, where you will see an Exclude Categories drag-and-drop option field: https://i.imgur.com/HXetjor.png
Drag the categories to the right and the posts connected with them should be excluded from the results then.
I'm sorry if it's a bit confusing, I'm planning to re-structure the options on the back-end a bit, as it grow quite a bit from the beginning 🙂Best,
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