Windows-designed and/or tzdb-compliant software can and does handle these changes regularly, so unless the implementation is bonkers (which means it is hardcoded and someone should be fired like this alarm clock designer: https://news.ycombinator.com/item?id=25647903), it is an embedded software, or it was literally hours before the transition, it should just work with a simple change in registry (Windows, usually handled by updates) or text files (tzdb).

DST dates already changed in 2007. But I guess that's 14 years worth of more bad implementations ready to go.

https://en.wikipedia.org/wiki/Energy_Policy_Act_of_2005#Chan...

There was a similar change in Russia and Armenia several years ago, and nothing fun or spectacular have happened. Only old computers without internet access had required manual update of clock settings.