I believe there's no direct way how to recognize inside the flow who already selected an option and who didn't. But if you're storing that information in a separate list, you could add a separate flow to send the reminders.
There would be 2 prerequisites (you could store the data in another SP list, let's call it Configuration list):
List of users who should respond
Date when the email with options was sent
Then it would be a scheduled flow that would run every day:
check if today is 24 days from the day when the email with options was sent. If no, do nothing. If yes, continue:
compare the 2 lists - for each user in the Configuration list check if they already selected an option (they'll have an entry in the current SP list). If yes, do nothing. If no, store them in an array/string variable of 'users to remind':
send an email to the 'users to remind'
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