Hello, I just realised that nobody seems to have gotten back to you.
I assume that everyone is very different, given the variability of severity and symptoms at any given time. I don't think there could be a blanket suggestion of which exercises are "good" and which ones were "bad". The considerations for someone with an ostomy may be quite different for someone without an ostomy, for instance.
In general, I know that's it's common to experience joint pain, so "high impact" exercise like running may aggravate that. I've often heard swimming suggested as a good form of exercise when experiencing joint troubles. I wouldn't know personally, since I never learned to swim, for some reason!
I know that higher intensity exercise can be difficult when having an acute flare of symptoms, given the fatigue, pain, and difficulty consuming enough calories. I've been advised to try to continue with lighter exercise (e.g: walking) when experiencing a flare.
I have had some suggestions for exercising after having open abdominal surgery for Crohn's, which many people require. Exercises which put pressure on the core abdominal muscles may increase the risk of hernia, so I was advised to refrain from strenuous core exercises (e.g: sit-ups) for a while after surgery. I imagine that the risk of developing a hernia diminishes as the abdominal muscles heal, but I'm not entirely sure about that. I currently have few symptoms of active disease, and am able to lift dumbbell weights and do cardio exercises without notable difficulty or pain.
As always, it's good to speak to your doctor about healthy exercise. I imagine they'd be more than happy to suggest something based on as assessment of your condition. Some people can even perform at a very high level: there are Olympic weightlifters with Crohn's!