This discussion actually surprised me because in my extended family I have a relative with Chrohn’s and 2 with ulcerative colitis (on different sides of the family and one related via marriage — none are related to each other), and none of them keep it secret. They’re not wearing signs or shouting from rooftops, but they’ll mention it casually in conversation, reference their medications or diet restrictions, etc. I never thought of this as something that is kept so secretive until I saw this thread.
As far as shidduchim, 2 are marrying off their kids already and it doesn’t seem to be an issue, and the third has a few siblings who got married after him and it never came up either. Maybe in Chassidishe circles there is still more of a stigma attached to medical conditions, and B”H 2 out of the 3 have very few flare ups, so maybe that is a factor?