I have felt a bit the same with my max HR dropping to quite a bit below what it used to be, so that if I am trying to go at the same speed as before, then I am closer to max effort.
But I suspect that losing just 3 kg (never mind 10!) would make a HUGE difference to you. So maybe set yourself some goals that aren’t too far out of reach and see how you get on from there.
BTW I am probably 10 years older than you from the sounds of it. 40 is way too young to think about stopping