I’d say it’s an error in your date format, though use of forward slashes is more ‘pythonic’.
timestamp = system.date.format(system.date.now(), 'YYYY-MM-dd_HH_mm_ss')
filepath = 'C:/myExports/{}.csv'.format(timestamp)
print filepath
>>>
C:/myExports/2022-02-10_14_09_28.csv
>>>