Theoretically (pay attention to the theory of wearing, not fashion), a single-breasted suit (double-breasted suit must be buttoned) can be buttoned as long as one button is not buttoned, remember not to button it all. In other words, if you want the last button to be unbuttoned, then the top button should be unbuttoned. It's normal for the lower part of your tie to be exposed. I've seen people put ties in their pants. There is no doubt that it is purely disgusting, which is the practice of farmers.
Now let's talk about my suggestion: if you are a single-row three-button suit, only buckle in the middle, not buckle up and down, which will look fashionable and natural; If it's two buttons, the top button. Also, naturally unbutton all the buttons when you sit down, and then button them when you stand up and leave, which will look like a gentleman.
Finally, slimming suits are popular now. I'd rather wear a smaller one than a bigger one!