So sorry to hear of your problem. I wish I could offer different advice but think the previous posters have it covered (although I do disagree with suddenly sleeping a 6 year old house Labrador outdoors!). If it’s any comfort, we’ve had Labs for years and, in my experience, they can suddenly change nighttime habits as they age (don’t we all!). Our current pair (approaching 9) have started to bark sporadically overnight. It doesn’t appear to be in response to anything in particular (eg foxes - we’re rural) and they aren’t upset, so there’s nothing to be done. I think if you monitor his eating habits, then just leave him be, he may stop of his own volition. You could, of course, install a dog flap (we did in previous homes) but, given the Lab’s size, it can become a ‘burglar flap’, as we discovered to our cost ... good luck!