WION recently reported that uncovered past audio tapes confirmed that in exchange for German reunification, NATO would not nove one inch closer to Russia.
And Gorbachev himself, who was the recipient of that alleged promise said that it was intended and understood as only a short term promise applicable only to East Germany, and that subsequent NATO expansion didn't violate any alleged agreement.
https://www.brookings.edu/blog/up-front/2014/11/06/did-nato-promise-not-to-enlarge-gorbachev-says-no/
In any case, under the U.S. Constitution, congressional action is required before any agreement made by a President - much less a Secretary of State - is binding. We knew that, the Soviets knew that, and the fact that the alleged promise wasn't put into a formal written agreement or treaty proves it was only a short term promise not intended to bind subsequent Administrations.
It's the same reason we weren't bound by Clinton's signature on Kyoto, or Obama's signature on the Paris Climate Accords.
I remember it being mentioned on the national news at that time.