20 Kgs does sound rather a lot but then they do vary in build quite a bit. I think, like us, they tend to put on weight with age and also they‘re rarely quite as active as in winter as in the summer months.
Certainly foods vary so its probably a good idea to have a look at the nutritional values incl. fat and also treats and snacks are very often VERY high in fats, - I used to give Humphrey dried pigs and cows‘s ears until he started putting weight on and I looked at the fat content and was horrified, he now gets a rabbit‘s ear occasionally but they‘re not so bad. Also, keep a check on the ‚extras“ - OH is forever passing the dog titbits but they mount up......
I give lots of vegetables to bulk up his food and he get raw carrots, apples etc instead of snacks.
It does seem to be a constant battle, particularly at the moment as he‘s not very mobile and they do like their food
but there are ways of cutting down on the calories without them going hungry.