If you"re seeing one question at a time while the rest questions are greyed out and keep seeing a Next Question button after every/some questions, it means you have Auto Advanced turned on in your survey.

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Auto Advance is a feature that shows the respondent one question at a time and as the respondent answers questions the survey will move to the next question automatically but this feature does not support all questions and hence unsupported questions are shown with the Next Question button below them.

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Next Question button can be removed but turning off the Auto Advance feature, please go to Design >> Display Settings >> Under Display Settings please scroll down to see Auto Advance and turn off the toggle & hit Save.
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Screenshot for reference - https://monosnap.com/file/KKKcuQRf9cUil2r34ka0pSyerEC5e9