It all depends on what you’ll be eating for the month, keep it clean and you’ll be good if you’re south Asian like myself and have a feast of fried foods and curry almost daily you will probably gain some weight.
I have had one Ramadan where I’ve actually managed to make the largest weight gain I’ve ever made within 30days, although I was consciously making the effort to put on weight and eat large meals for iftar and suhoor. My weight went from 76kg to 82kg by the end of the month. Always found it difficult to put weight on when I was younger so that was quite a shock for me.
Usually if I’m not fussed about what I’m consuming and eating whatever’s available I will still lose weight during Ramadan so I would say don’t worry to much. My biggest concern is taking a whole month off the gym so I do body weight exercises at home about 40mins before iftar