What is a software or app that extracts old flip phone data to a Mac via USB?
Have you tried contacting any local stores your phone provider has? It's becoming less common nowadays as basic phones are no longer the norm but back in the day they had a machine they could connect your phone to and transfer information out of it then on to a different phone.
Maybe you could call around to local stores and see if any of them still have such machine.
Otherwise, I did a bit of research because I used to know of some software that was for advanced phone modification before smartphones came around however it had a small feature to also see saved files.
I can't seem to find the software I remember using anymore, however I did find BitPim:

BitPim is a program that allows you to view and manipulate data on many CDMA phones from LG, Samsung, Sanyo and other manufacturers. This includes the PhoneBook, Calendar, WallPapers, RingTones (functionality varies by phone) and the Filesystem for most Qualcomm CDMA chipset based phones. To see when phones will be supported, which ones are already supported and which features are supported, see online help.
http://www.bitpim.org/

It seems very similar to the software I used to use, however I've never used it before so I can not offer any help with it other than this YouTube video I found.