( https://www.howtoforge.de/anleitung/was-ist-umask-unter-linux/ )
( https://linuxize.com/post/umask-command-in-linux/ )


*****   login shell
( https://forums.linuxmint.com/viewtopic.php?t=332252 )
.
In my /etc/login.defs there is a comment for umask:

# If USERGROUPS_ENAB is set to "yes", that will modify this UMASK default value
# for private user groups, i. e. the uid is the same as gid, and username is
# the same as the primary group name: for these, the user permissions will be
# used as group permissions, e. g. 022 will become 002.