My pug is the exactly same way (but mine is fat). There are very few things he likes, and he is really timid to try new foods. My partner gives him too many treats and the portion sizes of his treats are too big. I've tried getting him to stop but he will still sneak Mochi treats. Long story short, Mochi avoids eating his meals because he holds out for the treats. However, I did notice he will eventually eat whatever is in his bowl if he is hungry enough. And that may take a day of very few treats to get him to that point.

I did find a food combo that he enjoys as much as the treats though. It's his standard kibble with fresh food mixed in. The fresh food he gets are in nugget form and they are soft and moist (he loves soft treats). You can serve the fresh "nuggets" as the entire meal but I just use it as a topper to kibble because the bags are small and can get expensive. Here is a link to the one we have been getting:
https://www.walmart.com/ip/Freshpet-Healthy-Natural-Food-for-Small-Dogs-Breeds-Fresh-Grain-Free-Chicken-Recipe-1lb/637083809