The last change to how Solus sets directory permissions was made in 2018, so this probably wasn't caused by an update
The permissions are set in baselayout/actions.py
https://dev.getsol.us/source/baselayout/history/master/actions.py

From what I can find there is no standard for this. Ubuntu uses 700. RedHat and derivatives use 550.

There is another consideration, we recently changed user home directories from 755 to 770 - https://dev.getsol.us/T10379
Would similar reasoning for that change apply here?

It definitely has been changed (on my system) by the update I run today (where btw. baselayout was updated from 1.8.0-64-1-x86_64 to 1.8.0-67-1-x86_64).

One can easily check like this:

# chmod -c og= /root/
mode of '/root/' changed from 0755 (rwxr-xr-x) to 0700 (rwx------)
# eopkg install --reinstall baselayout
[...]
# chmod -c og= /root/
mode of '/root/' changed from 0755 (rwxr-xr-x) to 0700 (rwx------)

While 0770 wouldn't be a problem (as /root/ is root:root), others shouldn't be able to have any access to /root/.

@TClark77

I think we'll want to chmod -Rc 0770 /root during baselayout creation (to be consistent with /home/foo permissions), since it looks like the wrapped mkdir command is indeed using a default umask of 0755 like I idly speculated a day or two ago.