Everyone really is different, I don’t think you’ll find a single solution for the masses.
The majority here seem to agree on an ‘eat less, move more’=calorie deficit (abs are made in the kitchen) solution.
I had belly fat through most of my 40’s (I still have a little, but I’ve got clearly visible abs now). My results came by cutting out booze (over a year ago for mental health reasons).
Once I cut out alcohol I lost 2 inches off my waist in about 4 months (putting me back to a 34″ waist which is what I was in my 20’s and 30’s), with no other changes in my life.
FYI I’m late 40’s, 6’3″ and weigh 85kg but want to get that to 90kg, I cycle and row for cardio, and lift weights for stress relief.
I walk my dogs an hour or 2 most days and I always aim to consume more calories than I need as I have a hard time maintaining weight, that’s why I think it was only the alcohol that caused the spare tyre.
I logged my food until I became good at knowing when I’ve got through 3K calories each day, so I can relate to grazing on nuts and fruit in-between meals.
My 2 brothers seem to have the same metabolism, however my older brother does loads of cardio and is leaner than me, and my younger brother doesn’t exercise and has a desk job and a fantastic beer gut! So genetics only get you so far!
I’d stick with what you’re doing, it should work!