Your information is outdated. It used to be common belief, the idea that you either gain both fat and muscle at the same time or you lose both, but it no longer is due to the vast numbers of people who have gained muscle while losing fat, backed up with photo evidence, logs, et cetera.
Part of the reason for your misconception, a common one, was that body builders were going on psychotic bulking diets like GOMAD, and/or drinking multiple "MASS GAIN !!!!!" shakes a day which have whey protein mixed with nonsense ingredients like dextrose. I mean yeah, if you go on meal plans like this:
https://www.mealplansite.com/sports/bodybuilding-new-gain.aspx
You might gain 15 lbs of muscle, and 30 lbs of fat. It fits the traditional viewpoint that dominated in the 1990s.
But it's not ideal.
Here's a supplement that will fit your world view:
View attachment 54654
It has 1,250 calories (!!!) per serving. It is intended to help put on "serious mass" as per the title. And IMO that's what it's going to do, as in you'll be putting on serious fat mass.