Did Congress agree with it? Because if congress did not approve than it was not signed be the USA.
I think, legally, it has the same effect as an executive order which has not been revoked by a later administration.
Senator Biden was on the Senate Foreign Relations committee in 1994, so presumably knew of and approved of Pres. Slick's Budapest Memorandum promising to defend Ukraine in exchange for Ukraine giving up its nukes.
The language of the Budapest Memorandum is not the same as, for example, NATO's Article 5, in which an attack on one is an attack on all, but neither is it meaningless, to be sloughed off as if non-existent.