In Russian, it would depend on the last name in question specifically, as well as the gender of the person talked about. I am a native speaker, but I don't know

In Russian, it would depend on the last name in question specifically, as well as the gender of the person talked about. I am a native speaker, but I don't know which specific grammar rule governs it. For example, Zuckerberg absolutely gets declined and gets that "oo" at the end. "To Mr. Dorsey" doesn't get changed (i.e., no added "oo" at the end) due to declining (but it still gets declined), while "to Mr. Smith" definitely gets that extra "oo" at the end due to declining. But "to Mrs. Smith" is unchanged after declining, so it doesn't get that same "oo" ending.