Really depends on the gun to some degree. There’s collectibles that are worth more left alone, especially old stuff pre modern ammunition. But lots of old but not that old stuff its more or less expected you’ll fire it to test it works on receipt.

"old but not that old" is essentially saying it's not an antique.

There are plenty of guns running around that are over 100 years old that are surely an antique by anyone's definition, but are safe and reasonable to show with modern ammo. Pretty much any gun of that age, unless it was some kind of commemorative thing from the start, is going to have plenty of rounds through it already.

For example - an M1903 is an antique by any definition, and you'd be hard pressed to buy one today that's unfired.