i've noticed many times that applescript doesn't take this syntax

Make a note to post actual code, never pictures of code - you aren’t going to get many replies when people have to type in your script or debug formatting errors from the text recognition framework.

The error is from trying to use Reminders to get the start date of a Calendar event. You need to target the appropriate application to use its terminology, for example:

-- Set the names of your calendar and reminders
set calendarName to "appts"
set remindersName to "appts"

-- Get the current date and time
set currentDate to current date

-- Get the events from the calendar
tell application "Calendar"
   set calendarEvents to every event of calendar calendarName whose start date is greater than currentDate
   repeat with theEvent in calendarEvents
      set eventTitle to summary of theEvent
      set eventStartDate to start date of theEvent
      set eventNotes to description of theEvent
      if eventNotes is missing value then set eventNotes to "(no notes)"
      
      -- Create a new reminder with the event details
      tell application "Reminders" to tell list remindersName
         make new reminder with properties {name:eventTitle, due date:eventStartDate, body:eventNotes}
      end tell
      
   end repeat
end tell