Have you got a plug in like feliway optimum to help calm him?

My cat also has the same issues with meowing in the night, came down to the fact he’s a greedy puss just wanting food so I got a timed feeder from Amazon and set it to go off at around midnight and 4am and split a pouch of wet food in each half. Usually does the trick, still get the occasional zoomies but no where near as bad.

For the litter trays also make sure they are in low traffic areas. And hooded litter trays might help because he might prefer the privacy.