SUMMARY

I set my display clock to only show UTC, while my system timezone is set to US Eastern Time. I knew the end of DST was coming today, 2025-11-02, but last night before the switch at about 2025-11-01 23:50 EDT, I noticed that the clock displayed an incorrect time for UTC: 2025-11-02 2:50 UTC. As EDT is UTC-4, this is a clearly incorrect result. My theory is that the UTC clock is being updated by adding 4 hours to EDT, which crosses the boundary when the clock is switched to EST at 02:00 EDT / 01:00 EST, so it subtracts 1 hour to compensate. 

STEPS TO REPRODUCE
1. Set primary timezone to "America/New York" or similar timezone, e.g. through timedatectl.
2. Set Digital Clock widget to display UTC.
3. Set system time to 2025-11-02 03:00 UTC, e.g. through timedatectl.

OBSERVED RESULT

UTC is an hour earlier than it should be while system clock is in daylight time.
After the switch to standard time UTC is displayed correctly.

Output of date:
2025年 11月  1日 土曜日 23:07:41 EDT

Output of date -u:
2025年 11月  2日 日曜日 03:08:07 UTC

Output of timedatectl show:
Timezone=America/New_York
LocalRTC=no
CanNTP=yes
NTP=no
NTPSynchronized=no
TimeUSec=Sat 2025-11-01 23:03:43 EDT
RTCTimeUSec=Sat 2025-11-01 23:03:44 EDT

Clock widget display:
2:09 (UTC)
2025年 11月  2日 日曜日

EXPECTED RESULT

UTC is always displayed correctly.


SOFTWARE/OS VERSIONS

Operating System: Arch Linux
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.18.0
Qt Version: 6.9.2
Kernel Version: 6.12.50-1-lts (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 5700X 8-Core Processor
Memory: 32 GiB of RAM (31.3 GiB usable)
Graphics Processor: AMD Radeon RX 6700 XT

ADDITIONAL INFORMATION

My date language is set to "ja_JP.UTF-8" and the digital clock is set to display 24hr time, but I don't feel that should affect anything.