Invited to civil wedding between lapsed Catholics; go or not go?

As the title says, if you’re invited by a friend/colleague/relative to their civil wedding celebration, and they — bride and groom both — are both lapsed Catholics, where they are only having a civil marriage with no church or sacrament at all, do you go, or not go? Is it scandalous to go? Uncharitable not to?

Edit: Thank you all for your answers. I found this helpful article written by a priest, published last year (this would be “Case 3”): https://www.simplycatholic.com/may-i-attend-the-wedding According to this, it depends on whether the couple know it’s a sin, and the likely outcome of attending or not attending.