File and directory permissions Mautic docs not clear

Your software
My Mautic version is:2.16.0
My PHP version is: 7.2.27

Your problem
My problem is:

The mautic post here:

states that file and user permissions should be:

The owner of the files is probably going to be `www-data` in a VPS/EC2/Droplet environment, and your user ID in a shared hosting environment.
In a shared environment, start with this:
cd /var/www/
chown -R $USER:www-data .

However, depending on how a user logs into a system via ssh for example that would have an effect on $USER. If a user logs in as root $USER would be root, if a user logs in as a plain-vanilla user it could be anything.

So if it is root vs. plain vanilla user, what are the consequences of this difference?
These errors are showing in the log:

Steps I have tried to fix the problem: read the mautic documentation which does not explain what kind user $USER is.