@hornyathome
I feel for you. I know what it's like to be in a sexless and passionless marriage. 
You have to demand sex, and he will (I expect reluctantly) "comply"?
He made more effort before and in early marriage? (also before children?)
He masturbates, but won't have sex with you?
What on earth is the matter with this man?
I'm no doctor, but I don't think this is a low testosterone thing. Typical symptoms of that are: -
Reduced sex drive.
Reduced erectile function.
Loss of body hair.
Less beard growth.
Loss of lean muscle mass.
Feeling very tired all the time (fatigue)
Obesity (being overweight)
Symptoms of depression.
If he masturbates a few times a week, then he has a (reasonable) sex drive, and can obviously get and maintain an erection. (you don't say if he has a problem when he does "comply")
You also mention no romance - I wonder if there is more to that particular story?
Sounds like he has checked out of the relationship, at least from an intimacy perspective.
Is it possible that, now that (in his mind) his "job" as far as fathering children is done he now sees you as a replacement mother, rather than a wife and continuing sexual partner?
Would he consider going to couples therapy with you? I know they are extraordinarily busy , as lockdown has put enormous pressures on relationships, but if you want to change things, this might be the way to go.
Conversely, would you consider going elsewhere for intimacy? (I discussed an open marriage with my XW, but we decided it wouldn't work for us.) It's not a path to be trodden lightly, but I'm certain you could find any number of men willing and able.