FIA,
The concept of hefsek that I explained is an explanation for a minhag, I don’t know of any poskim that hold it is required for someone who doesn’t have the minhag.
With regard to married couples holding hands in public, there is definitely a strong argument that it is mutar. The issur of chiba b’rabbim is that it might cause hirhurim to those watching. The issue is what level of chiba might cause hirhurim. The Aruch Hashulchan writes that one should avoid “chiba yiseira” in public.
Arguably holding hands is not “chiba yiseira.”
Note that the Shulchan Aruch does not bring down the shita that chiba b’rabbim is assur (it is mentioned as a “yesh omrim” in the Rama).