MacOS – Relocated items after macOS update to 11.3.1

big surmacos

After updating my macOS to 11.3.1 from 11.3, a directory named Relocated Items appeared on my desktop.
A document in that directory explained a bit about what's going on. I will attach the text of the document below.

so I viewed a diff between /etc/group and ~/Desktop/.../group.system_default and saw that
the line containing _trustd:*:282:_trustd exists in group.system_default but not in /etc/group.
Another odd thing I realized is the 'Date modified' on the file on group.system_default is 1. Jan 2020. This computer and the install are both from 2021.

Can somebody explain what is going on? I am not sure which of the files came with the macos-update and which I suposedly modified in the previous version.
I also don't understand what _trustd:*:282:_trustd means.

Document in Relocated Items Directory

During the last macOS upgrade or file migration, some of your files couldn’t be moved to their
new locations. This folder contains these files.

Configuration files
These configuration files were modified or customised by you, by another user or by an app.
The modifications may be incompatible with the recent macOS upgrade. The modified files are
in the Configuration folder, organised in subfolders named after their original locations.

To restore any of the custom configurations, compare your modifications with the configuration
changes made during the macOS upgrade and combine them when possible.

Configuration files with the suffix "system_default" were edited or customised but the changes
were allowed to remain installed. The system_default version of the file is provided to
demonstrate what the Apple-supplied version of this file would look like.
It is recommended you compare the two and evaluate whether you wish to integrate any changes
Apple may have made to the default version.

Best Answer

To your question, which file is the modified one, the document you've added already explains that:

Configuration files with the suffix "system_default" were edited or customised but the changes were allowed to remain installed

...which means your current file "group" is the modified one and "group.system_default" is the default one, but wasn't installed, because the changes to "group" were allowed.

_trustd:*:282:_trustd

...is a user of the same named group on your computer, as also found in "Directory Utility.app" (for which you can search in Spotlight).
"282" is the "PrimaryGroupID".

The man pages for trustd mention:

trustd(8)                 BSD System Manager's Manual                trustd(8)

NAME
     trustd -- Daemon and LaunchAgent that performs trust evaluations

SYNOPSIS
     trustd

DESCRIPTION
     trustd provides services for evaluating trust in certificates for all processes on the system.

     This command is not intended to be invoked directly.

BSD                               May 7, 2021                              BSD

Who initiated the changes, or why, I cannot say - I would think you yourself should have a better idea, if you've done any modifications, or which application you've installed, that could have changed the "group" file. Or maybe somebody else here knows.

About the date: if you look through the system volume, you may find that pretty much all system files have the same modification date (which is new in Big Sur with its boot snapshot).

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