I believe that you are adding to Scripture.
I don’t see that it is addressing widows.
I believe you are mistaken Steve. You seem to be assuming that "brother's wife" in Leviticus 20 verse 21 only refers to the present wife of a living brother, not his widow,.or divorced ex-wife.
If it is any comfort, Hunter Biden apparently agrees with your view.
I don't think the larger context supports that assumption.
Following your logic, the following relationships would also be permitted for similar reasons.
1. His stepmom if his father has died or divorced her (verse 11). She isn't his father's wife anymore if the father is dead or has divorced her.
This is likely the situation Paul was dealing with in 1st Corinthians.
2. A man and his former daughter in law if the son has died or divorced her (verse 12). She isn't his daughter in law anymore after death or divorce.
3. A man and his former mother in law if his wife (her daughter) has died or divorced (verse 14). He isn't having them both at the same time. She isn't his mother in law any more.
4. A man and his aunt by marriage if his uncle dies or is divorced (verse 20). She isn't his uncle's wife any more.
I do not think your interpretation holds up under scrutiny. I believe all of these relationships are prohibited.
Why are any of these laws given in the first place? The stepmom, sister in law, aunt, and daughter in law issued are already covered under the basic commandment against adultery with another man's wife.
Your view makes all of these additional laws pointless in their redundancy.
There seems to be another principle at work here, against the sexualization of close relatives (including in laws).
The levirate law is an exception. In that case, the importance of raising up seed for the deceased man takes precedence.
As far as I know, the position I am taking is the nearly universal understanding of the Christian church throughout history, and also the nearly universal understanding of Jewish rabbis.
That doesn't mean I'm right, but I think there is a pretty good likelihood.