As @jphermans said. Be sure not to change the /data folder right from the :I have one question:
what exactly should I do to have my data to be stored in that local "/data" subfolder? I configured it as you described (the only difference, I did not named it /data, instead of this I used /mydata), but In File Station under docker/bitwarden I cannot see any subfolder nor data files...
Thats the value of the folder inside the container thats actually holding the data. So change only the left side (your host side) location.