This guide, helps setting up umask for users and help setting correct permissions for files in shared directory. This also mitigate a know Gnome bug, that ignores umask and enforces umask 022

Create the user group and assign the group to the user:

sudo addgroup group
sudo usermod user +aG group

Fix the broken umask in Gnome environment. Edit the Umask option to whatever you desire.

Creating folders for new config files:

sudo mkdir -p /etc/systemd/system/display-manager.service.d/  /etc/systemd/user/gnome-terminal-server.service.d

Content of /etc/systemd/system/display-manager.service.d/umask.conf

[Service]
UMask=007

Content of /etc/systemd/user/gnome-terminal-server.service.d/umask.conf

[Service]
UMask=007

Setting dbus to override umask, for current user only. Run this on each user. Insert the following, after the command:

systemctl --user edit dbus

[Service]
UMask=007

Setting personal umask permission for current user only Add this to the end of ~/profile

umask 007

Setting global umask permissions for all users. Add this to the end of /etc/profile

umask 007

Setting directory permissions:

sudo chmod 770 /zfspool/dataset
sudo chmod g+s /zfspool/dataset
sudo chown user:group /zfspool/dataset 

Setting ACL enabled on ZFS dataset.

 sudo zfs set acltype=posixacl zfspool/dataset

You can check all settings on dataset by typing

sudo zfs get all zfspool/dataset