Hi Nuray,
It seems like this is by design and there is no option to turn the option off globally I am afraid:
https://www.reddit.com/r/Outlook/comments/wfr0u9/unable_to_turn_off_responses_required_for_a/
Please click the Help option in Outlook > Send feedback to let the relevant teams know.
I hope this information helps. If you have any more questions, don't hesitate to reach out.
Otherwise, please take a moment to rate the answer. Wishing you good luck!
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