Is it true that "marriage is honorable among ALL, and the bed undefiled" according to Hebrew 13:4?

Allowing for the fact that "ALL" is understood in the authentic context of the Judeo-Christian faith tradition; meaning all hetero couples.

Hetero marriage, yes, if the spouses honor the covenant and each other.

The English language has changed quite a bit since the KJV was translated in 1611.  The NIV says in wording that is easier for us to understand today.

 "Marriage should be honored by all, and the marriage bed kept pure, for God will judge the adulterer and all the sexually immoral."

It is not saying that marriage IS honorable and the bed undefiled.  It is saying that as Christians we should honor marriage and keep it undefiled.  Thus the second half of the passage which you did not quote.

It is true, in fact a more correct translation would be that “the marriage bed is undefilable”

Yes and marriage is the marriage of one man and one woman in Holy matrimony but whoremongers and adulterers will be punished.  God will punish all other manners of sexual devices or sexual behaviors.

Since the Bible approves of slavery, rape, beating slaves, and all kinds of bigotry and hate, I really don't give a damm what it says about anything else.  It has no moral compass and it is nothing but a POS Cult Book.