The file /etc/X11/xdm/Xsetup contains commands that are executed by XDM before displaying the login screen. This file can be used to set the background image, color, or run other programs on the X display. The other files are either not related to XDM or do not exist by default. Reference:
XDM - ArchWiki
Customizing the XDM Login Screen | Linux Journal

files
Explanation:
The keyword files must be listed in the hosts option of the Name Service Switch configuration file in order to make host lookups consult the /etc/hosts file. The files service specifies that the local files, such as /etc/hosts, should be used as a source of information. The order of the services on the line determines the order in which those services will be queried, in turn, until a result is found. For example, if the hosts option is set to:
hosts: files dns
then the /etc/hosts file will be searched first, and if no match is found, the DNS server will be queried next. If the hosts option is set to:
hosts: dns files
then the DNS server will be queried first, and if no match is found, the /etc/hosts file will be searched next. References:
* LPI 102-500 Exam Objectives, Topic 110: Network Fundamentals, Weight: 4, 110.3 Basic network troubleshooting
* LPI 102-500 Study Guide, Chapter 10: Network Fundamentals, Section 10.3: Basic Network Troubleshooting, Page 125-126
* nsswitch.conf: Name Service Switch configuration file

systemd-journald is a system service that collects and stores logging data from various sources, such as kernel, user-mode programs, and services1. It creates and maintains structured, indexed journals that include metadata and binary data where necessary1. The journal format is secure and unfakeable1. systemd-journald is not incompatible with syslog and can coexist with it. It can forward log messages to a syslog daemon for further processing, filtering, or storage2. This can be enabled by setting the ForwardToSyslog option to yes in the /etc/systemd/journald.conf file2. systemd-journald does not only process messages of systemd, but also messages of any other tools that use the standard logging interfaces, such as syslog(3), sd_journal_print(3), or systemd-cat(1)1. systemd-journald also supports syslog facilities, such as kern, user, and auth, which are used to specify the type of program that is logging the message3. These facilities can be used to filter the journal entries by using the -p or --priority option of the journalctl command4. For example, to show only kernel messages, we can use journalctl -p kern4. Reference:
systemd-journald.service
Introduction to the Systemd journal
systemd/Journal
journalctl: Query the systemd Journal