Hang around me for a while!
Actually, it's not a stupid question at all. Being too heavy or too thin can be unhealthy.
Really, it's just a calories game. You just have to eat more calories. Personally, I think you're wise to avoid "junk" foods, though many can be high in calories. If it were just calories, maybe it wouldn't be too bad. But, many junk foods contain other problematic compounds. So, I commend your decision.
Here's one of many articles to consider:/www.healthline.com/nutrition/18-foods-to-gain-weight
I consider products like protein powders to be processed/junk foods, too. But, you'll have to make that decision for yourself. If you search Google for something like "calorie dense foods for weight gain," you will find lots of articles and opinions.
While High-Fat and Ketogenic diets are en vogue now, I wouldn't recommend them. We need fat in our diet, no doubt. But, some people take this to extreme by eating entire sticks of butter, infusing their coffee with butter and coconut/MCT oil, eating lots of fatty cuts of meat, lots of eggs, eating coconut oil by the spoon, etc. Maybe these will turn-out to be a revelation (kind of like this scene in Woody Allen's film SLEEPER
), but I think the mounting opinion and evidence is suggesting otherwise. But, I'm no Doctor or Dietician. This is just my opinion.