Dear Rabbi, Why do some people say b’Reshus before hamotzi. Is this actual halacha or just a minhag?

Shalom, Thank you for your question. The question of asking permission to say the blessing by saying "BeReshut" (that is "With your permission") is mentioned in early sources. For example, the Rema in his notes to the Shulchan Aruch (Orech Haim 174, 8) talks about the situation where one person wants to say a blessing, for themselves and all those present, over wine in the middle of a meal. In order to get everyone's attention the Rema writes that he should say "Sevri Rabotia" before saying the blessing. He adds that in such a situation on should not say "BeRashut", as he needs to ask them do they "intend" to be part of his blessing, and not just that they give him permission to be the one to say the blessing. The Mishna Brurah (ibid 47) explains that BeReshut is the appropriate wording to use when one wants to say a blessing that covers other people (ie with your permission I say the blessing for all of us), however in the case of the blessing for wine in the middle of eating, one also needs to ascertain that all those present actually want to stop eating and listen to the blessing, so one is forced to use the language of Sevri (ie do you intend to be part of this blessing?). From here it is clear that before saying Hamotzi for a group, when it is clear that they all intend to be covered by the blessing, (as they aren't in the middle of eating or any other activity), one only needs to ask for their permission – Be'Reshut. However, this is not universal practice, and many people do not say BeReshut (or Sevri). The Sephardim use BeReshut before many mitzvot – such as Sefirot HaOmer and others. The Ashkanazim tend not to use BeReshut except before HaMotzit, and even then it is not said by everyone (as you've probably noticed). It is perfectly fine to continue whatever custom you have about this – either to say it or not, as the case may be. Blessings.