We are not allowed to say sad news on Shabbos.
This past Shabbos, would it be permissible to tell a gabbai making a mishabayrach for Rav Dovid zatzal not to do so? (The posek hador was niftar an hour before Shabbos and not everyone was aware of this.) Was it permissible for a rav to mention in his drasha something about the petira, or should one avoid discussing it at all and distressing people who may not have heard of it?
Is there a chiluk if the people already know about the petira, or if it’s news?
Since we don’t say thing on Shabbos that will cause people pain, it is better just not to talk about it. If the gabbai will include his name in the list of people for a mishebeirach, nothing terrible happened.
Regarding the Rov talking about it, we assume the Rov knows the halacha, and if he feels that it can be said, we can trust him.
Regarding Shabbos there is no difference between people that know the news and others, the idea is that when talking about it, it causes pain and anguish on Shabbos which we want to avoid, unless necessary.