Ok this is a double header:
Always be genuine in your words and actions. When you tell someone you are happy for them, truly mean it or don’t say it. Don’t say or do things because it is the proper or politically correct thing to do.
I often wonder about people who are serial wedding/engagement party/baby shower attendees. I wonder if they are truly enjoy always celebrating someone else, or do they attend because it makes them look like the great, supportive friend and less like a hater. Or better yet, is the attendance a social investment so when it is their turn for their wedding, everyone will be willing to show up for them because they showed up in the past?
I urge you to never do things out of etiquette, political correctness or a social insurance policy. Every move you make you want it to be authentic. You will know it is authentic because you will literally feel the joy of the person you are celebrating as if if was your own. If you cannot connect in that manner, think about whether it is the right move at the time. If attending an event celebrating someone else’s milestone is more of a chore than an act of vicarious joy, you may want to opt out.