Demand Barking - HELP

My 4-month old puppy won’t stop demanding barking. He doesn’t really bark at other dogs and rarely at other people, only my partner and I. We’ve tried all the methods - from reverse time-outs to ignoring - and it seems to have gotten worse. We cannot figure out any specific triggers as it’s with everything. We’re in an apartment and cannot have him barking like this, as often as this, so we would like to get this figured out.

Any tips is much appreciated!

PS: He always gets plenty of exercise, naps, and mental stimulation throughout the day.