I'm sorry - that must be so hard to hear after such a long time together.
Here's what I woudl do if DH said that to me, and our life was in the shape you say yours is in.
I'd take a really hard look at my own life - where I'd got stuck and stale, and I'd start making changes. I'd begin by getting seriously fit - lifting weights, going for walks, runs, cycles, swims, boxing training, yoga, maybe some dance classes (men who can dance are very attractive.)
I wouldn't discuss it much, just start doing it. Start doing some other stuff too - some new hobby or training that you've maybe always been interested in.
If she is just bored and empty-nesty, then the newly energised you might become intriguing to her. And if she genuinely has run her course in your marriage, then you have the bonus of taking better care of yourself in a heartbreaking time, and having new things to distract you.
If she is open to it, you could discuss couples therapy or you could suggest creating bucket lists together and supporting each other in a year of fulfilling as many things from the list as possible. Show her you recognise that life as it has become recently isn't working for either of you and needs a big reboot.
You sound like you love her and I think I would take the risk of saying: life has been mega shit recently with Covid lockdowns, empty nest, struggling with menopause and weight gain. Before we ditch marriage and enter old age without the support of each other and a united family, let's at least have a go at having fun together and shaking things up.
But ultimately, if she wants to go, you are better off building a new life without her or with a new partner, rather than constantly jumping through hoops trying to please someone who isn;t interested.