When assigning the formula using xlwings in your code, the formula is being placed between curly braces {} because it is an array formula. To avoid this, you need to use the .formula property instead of .formula_array to assign the formula to the cell. Here's an updated version of your code:
# ...
# Load workbook
wb = xw.Book(output_file_path)
# Get the sheet
sheet = wb.sheets['RESULTS-ExcelVersion']
# Assign the formula to cell A9
sheet.range('A9').formula = '=IFERROR(SORT(FILTER(\'Fwd Data\'!B:P,\'Fwd Data\'!A:A=TRUE),2,-1),"NO RESULTS FOUND WITHIN THESE THRESHOLDS")'
# Save and close the workbook
wb.save()
wb.close()
# ...
By using .formula instead of .formula_array, the formula will be assigned correctly without the curly braces.
# ...
# Load workbook
wb = xw.Book(output_file_path)
# Get the sheet
sheet = wb.sheets['RESULTS-ExcelVersion']
# Assign the formula to cell A9
sheet.range('A9').formula = '=IFERROR(SORT(FILTER(\'Fwd Data\'!B:P,\'Fwd Data\'!A:A=TRUE),2,-1),"NO RESULTS FOUND WITHIN THESE THRESHOLDS")'
# Save and close the workbook
wb.save()
wb.close()
# ...
By using .formula instead of .formula_array, the formula will be assigned correctly without the curly braces.