TLDR-> play on no network vm os, use a uninstaller cleaner software to remove.
Not "hidden" per se, but there are folders and files made and then placed into the users folder (os-drive-letter:\Users\user.name\AppData\-local and -Roaming folders, for windows users probably the same for wine) as I have found the folder \WaysOfLife088) folder within each of the following directories after starting a new game and then "uninstalling" these folders and the sub folder files still remained.
Note did not use an uninstaller cleaner software (revo uninstaller) on first uninstall when I did on second uninstall it did find these folders and sub folders files and removed them.
but does make folder (within windows) here
os-drive-letter:\Users\user.name\AppData\Local\WaysOfLife-version-number-played\user data
with three (3) sub folders and three (3) files
and here
os-drive-letter:\Users\user.name\AppData\Roaming\WaysOfLife-version-number-played\
with nine (9) sub folders and two (2) files
Or played within a vm with blocked - no network interface enabled...