My wife & I have been married for over 40 years as well. And I guess yours & our relationships have similar problems except that, in mine, it's me that no longer has an interest in sex.

Similar to your wife, my own lack of interest in sex came to a head, so to speak, as a result of a medical / surgical issue. (But also, all of my life, I have struggled with gender identity issues. And that has played a role as well. But then, that's another whole story in-&-of itself.)

Honestly, I can't say whether or not your wife's refusal to "cooperate with you" is selfish or not. All I can say is that, in my own case, the interest (or desire perhaps) simply isn't there anymore. And so, to try to do it for the sake of my spouse (fortunately I don't have too) would simply be more emotionally / psychologically difficult than I could tolerate on an ongoing basis. So I must admit, I sympathize with your wife.

You mentioned you're looking for a therapist. And I think that's a good thing. I think about starting to see a therapist (again) myself from time-to-time. However, in my case, I always come to the conclusion I'm just too old to make it worthwhile. Plus there's nothing a therapist could say that would change anything anyway. It all just is what it is. (Hopefully you can have a different outcome.) I do think it's unfortunate your wife is taking the position she's taking with regard to her participating in therapy. But I understand that as well because my wife also refuses to have anything to do with therapy: individual, couples, or otherwise.

Under any circumstances, I wish you well. I'm sorry I don't have anything to offer that can be of help. But, hopefully, knowing there are others out there who have similar sorts of problems can at least be of some small comfort. My best wishes to you...