Files with memo extension can be encountered as old notes files from Memo app installed on Samsung Galaxy Avant.
MEMO file extension - Samsung memo file
What is memo file? How to open memo files?
File type specification:
File extension memo is known to be used for special memo notes created using Memo app on some older Samsung devices, for example the Samsung Galaxy Avant from 2014.
These .memo files looks like to be ZIP container that contain the memo notes in XML format with additional metadata files.