So, I finally figured it out. Probably just a bunch derps on my part:
1st: systemd-timesyncd wasn’t running, as seen via systemctl status systemd-timesyncd. This is usually started when you issue timedatectl set-ntp true, but for some reason it was inactive, even though I had invoked set-ntp true a couple of times already … no clue why. It’s active now, so I’m good, I think.
$ systemctl status systemd-timesyncd.service
● systemd-timesyncd.service - Network Time Synchronization
Loaded: loaded (/usr/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2022-03-21 16:25:18 CET; 19min ago
Docs: man:systemd-timesyncd.service(8)
Main PID: 330 (systemd-timesyn)
Status: "Daemon is running"
Tasks: 1 (limit: 8540)
CPU: 86ms
CGroup: /system.slice/systemd-timesyncd.service
└─330 /usr/lib/systemd/systemd-timesyncd
Mar 13 02:24:20 radonite systemd[1]: Starting Network Time Synchronization...
Mar 13 02:24:20 radonite systemd-timesyncd[330]: System clock time unset or jumped backwards, restoring from recorded timestamp: Mon 202>
Mar 21 16:25:18 radonite systemd[1]: Started Network Time Synchronization.
2nd: No drop-ins for /etc/systemd/timesyncd.conf existed and no NTP servers were set up in the “main” config file. I now manually set up four NTP servers in timesyncd.conf:
[Time]
NTP=0.arch.pool.ntp.org 1.arch.pool.ntp.org 2.arch.pool.ntp.org 3.arch.pool.ntp.org
3rd: This one was probably my biggest dumb-dumb—chronyd was installed, but not enabled.
sudo systemctl enable --now chronyd
After this, the time synchronization is now active:
$ timedatectl
Local time: Mon 2022-03-21 16:41:12 CET
Universal time: Mon 2022-03-21 15:41:12 UTC
RTC time: n/a
Time zone: Europe/Berlin (CET, +0100)
System clock synchronized: yes
NTP service: active
RTC in local TZ: no
Problem solved. Thank you all for your help, ideas, and patience. 