This isn't a direct answer, and I'm not an expert. I would say that increasing your total weekly volume should be one of the last things you should do to increase hypertrophy. Volume itself has pretty drastic diminishing returns, and early on is a good way to push, but it falls off fast for the effort involved. Sets 5-10 do a lot more for you than 11-20 (edited reps-sets).

I would focus on training sufficiently close to failure, them increase your frequency. If you can hit the same muscle 3x a week instead of 1 or 2x, it's going to be a much bigger difference than slamming more reps onto the same workouts.

With that being said, for increasing lifting stamina, I wanted to do it, I would make sure your nutrition is on target and get good rest, then just slowly ramp up the volume and see what you can handle and adjust accordingly.

First - everyone’s capacity is different; science discovers averages. There’s freaks who can do 20 sets and people who can do 5.

Over time you may be able to increase your tolerance slightly but recovery is ultimately a limited resource. Sleep, diet, and reduced stress outside of the gym are the only three things that I’m aware of that will help. When I had a job that basically was 2hrs a day, my diet was clocked in, and i was sleeping super regularly, I could do a lot more in the gym than I am now. I’m repeating a cycle from several years ago and I think my fatigue is more than just age.

The other area you can improve recovery and overall capacity with is performance enhancing drugs. That’s something I don’t really know too much about, but that’s the way I’ve heard it described - you heal faster, stronger.

Aside - last I read, ice baths are counterproductive to muscle growth because they reduce the inflamation that signals to growth. They’re useful for competitive scenarios where recovery is prime, but they don’t help with improvment. By all means keep doing it if you enjoy it. My strong preference is for a sauna!

"I pride myself on mental toughness so it’s not simply a matter of being lazy or cowardice." What? What does what you take pride in have to do with your performance? You could just be wrong. Your post gives the very strong impression of someone who's dramatically over thinking their training. If you're 40 and have been lifting for 10 months you probably literally don't know how hard you can push yourself, you haven't trained long enough or hard enough to have that experience.

Why worry about minutiae like optimal weekly set range for hypertrophy or your mesolimbic neurotransmitters when you're a novice lifter? You aren't eating in a calorie range for optimal hypertrophy no matter what set range you are at. By your own report what you're doing is working so just keep it simple. Don't go looking for problems you don't have.