Tonight, December 25, is Nittel Nacht, a gentile holiday.
On this day there is an extra abundance of impurity and a stronghold of Kelipa. For this reason, the Jews throughout the generations took various customs upon themselves which are followed until this day, in order to diminish the spiritual power of the impurity.
It is the custom of many Jewish communities to refrain from learning Torah on this night so as not to add strength to the forces of impurity – kelipa.
This is the Chabad custom as well, and it is said that the Rebbe Rashab was not happy with those students who ignored this custom and continued with their studies as usual.
The custom to avoid learning begins from the night of the Eve of the 25th of December until midnight. Starting from midnight, one may resume learning Torah, and there are no longer any restrictions.
Many have the custom to play chess on the night of Nittel.

True. Interesting of the various thoughts the Rebbe expressed concerning this night. One of course which he heard from his Father-In-Law concerning those that didn’t heed the restrictions for not learning.
In a general side thought. This photo you share playing chess is known not to be Nitel night. Rather when the Frediker Rebbe was in Germany in a health spa.
My intention is not for contradict anything rather as a side comment
Happy Chanukah to all.
The picture was in Parchtelsdorf, Austria not in Germany
THE PHOTO, THE ONLY ONE OF THE REBBE PLAYING CHESS, IMPLIES THE REBBE AND FRIEDIKER REBBE PLAYED ON NITTEL. IN FACT THE REBBE PLAYED ON AN ENTIRELY DIFFERENT TIME OF YEAR, ON THE ADVICE OF DOCTORS FOR THE FRIEDIKER REBBE, SO THE REBBE WOULD REST HIS MIND FROM THE HEAVY WORKLOAD WHILE RECOVERING FROM HEALTH ISSUES.
Is it a minhag to play chess in shul?
Is that really allowed by halacha?
An interesting video on the topic
https://youtu.be/qnSDWxPr1c0
I started listening but then i started wondering if learning on the topic was also learning?