You can set the permissions for the Home Directory to 7(That User)0(UserGroup)0(Others) - 700
This can be done in One Quick terminal command.
Launch terminal from app menu or with the keyboard shortcut ctrl+alt+t
Copy this and paste it in using right click or keyboard shortcut ctrl+shift+v
sudo chmod 700 /home/*
While you are in terminal... Let's elevate to Root (And now you will know how to do this) and launch your GUI tools while in Root to give them Admin Access:
sudo -i
Launch the file manager (Zorin OS Core)
nautilus
Now your file manager is elevated to root. Navigate in the left pane to "Other locations" and in the Right Pane to "computer"
Now, double click on the etc directory.
Scroll down past the Folders to the file named adduser.conf. You can also just type adduser into the file manager window and it should move to and highlight that file.
Right click that file and select to open it with Text Editor.
In the Text Editor, tap ctrl+f (Find) and search for DIR_MODE
It should take you to line 56. Change value from 0755 to 0700
Save and close.
Close the elevated file manager.
In the still open terminal, type
exit
and then close it. The above steps ensure that when a new user account is created, it is set to your preferred permissions by default. And... it gave you a bit of practice and familiarity.
I would recommend running the sudo chmod 700 /home/* on any already existing user accounts - just log into each one and set their permissions.
I could only speculate as to why this default is set to 755. So, I will tag @AZorin and @zorink if they can provide clarity to this default.