I took both tamoxifen for 5 years and anastrazole for 10. I never gained weight until a few years later when I was in a horrible accident, so I don’t think this will be universal.
There are a ton of variables in people, topping the list is genetics and daily life.
Then there is other medical conditions, jobs, family obligations etc, etc.
Are you concerned about weight gain, or gained weight on one of these drugs?