is it possible to create segment file name with date in the filename, instead of time in millis(long)... for eg.,testtable_OFFLINE_1637625600000_1637712000000_1469.tar.gz to testtable_OFFLINE_2021-11-01_2021-11-05_1.tar.gz

The segment name is derived from the data values in the date time column, so the only way (at least right now) to have the segment files named like that would be if you had a datetime column that stored the timestamp in a string format. I guess in theory you could create an unused column that has the date in that format, but I'd have to check how the segment file name generator works out which column to use as part of its name.