Our cat started meowling when he was older - 15+. We assumed it was a feline dementia kind of thing. He would shout up the stairs until someone said his name to him. He was calmer then, for a while, after he got some reassurance.
For us, it was both after we moved and when ours were older. Our girl cat used to talk a lot anyway but started yowling up the stairs at us in the night. We lost her last year at almost 17. Her brother, who barely even squeaked for those 17 years, then became very vocal and he now wanders around the house yowling at us in much the same way. I guess he just never needed to talk before as she did it for him!
So it could be moving and the lack of familiarity with the place or old age, I don’t think our boy cat’s hearing is great these days so that might be part of it too.
If you keep him happy - and hopefully pester him with conversation during the day - I think you'll find that nighttime yowling will decrease dramatically. He should get to the point where he'll think 'Oh Great. Lights Off. Now that ruddy woman will shut up and let me sleep.'
You have to work at it for a few days, though. Wake them up to talk, even.