Are you still allowed to make Havdalah today – Tuesday – for someone, being that Shabbos Havdalah was different, as it was Bein Kodesh Le’kodesh, from Shabbos to Yom Tov?

Permitted, and should say Nusach of Bein Kodesh Le’kodesh

Sources:

ראה שו״ע אדה״ז רצט,יא. ודון מינה ואוקי באתרין. וראה בארוכה באתרא דרב חוברת ג.