As above, just wear a suit with no tie. If everyone is more casual, take your jacket off, if they’re smart you can keep it on. All bases covered.
It helps if you’ve got a suit/shirt combo that isn’t overly business like (ie not black/dark grey). I’ve got a nice navy one that covers pretty much everything from weekend family celebrations to work stuff.
IMO “smart casual” was made up to protect events from people turning in tracksuit bottoms covered in paint and a 1993 Sweatershop jumper. Or girls dressing like they were turning tricks before they arrived.