I have recently stopped taking Carbimazole for Graves, and I'm afraid I did put on weight - about 3 stone.
However, that was over the lockdowns, and I was unable to go out because of exacerbated asthma that hit at the same time, so it's been really difficult to work out how much weight gain was from which cause. I really got no exercise for about 2 years, which is certain to have contributed to at least some of my weight gain, but if you ensure that you keep moving you'll probably find that you can keep on top of things.
The big worry is a thyroid storm (which didn't happen to me), but your endocrinologist will warn you about that and what to look out for.
I took Carbimazole for about 2 years, but I suspect that if all the consultations hadn't been over the phone it may have been a shorter period.