I know a couple of opera orchestra string players, which is kind of a big deal, they are near the top of their profession. They make a good living.
Yes, you can dress to the nines, if you like that, it’s great occasion, how often does a guy get to wear his tuxedo? (like most of the men in this pic).
But it’s not required. Lots of music lovers are there to listen, not to impress. I wouldn’t wear jeans or a baseball cap. Maybe “business casual” would be the minimum.
It’s fun as an event. It’s fun for see-and-be-seen. It’s fun for the music. If you are curious, just go!