Is it appropriate for a fatter person to wear a large size casual suit?

Of course it is not appropriate. The fatter the person, the more bloated he will look if he wears large-sized clothes. You can make a few suits that fit you, and the people who make them will measure your waist and bust. . . The measurements will be very clear, so there is no need to worry about not looking good when you wear them.

In short, I think so! Wear what you like and don't care what others think. Only when you are satisfied can you feel confident in your clothes. Just like if you like to wear oversized casual suits, then wear them. The most important thing is to be happy! However, my side advice is: if you want to wear a suit, you should go to the store to have it made, that way it will fit you best.