This list ignores the moon rock moons, for obvious reasons. I count multi-moons as one each.

Cap Kingdom:

All except for 13: Taxi Flying through Bonneton, 16: Peach in the Cap Kingdom and 17: Found with Cap Kingdom Art are available during the game. That’s 14.

Cascade Kingdom:

All except for 19: A Tourist in the Cascade Kingdom, 21: Peach in the Cascade Kingdom and 23: Caveman Cave-Fan are available. That’s 22.

Sand Kingdom:

All except for 64: Jammin’ in the Sand Kingdom, 65: Hat-and-Seek: In the Sand, 67: Binding Band Returned, 68: ‘Round the World Tourist, and 69: Peach in the Sand Kingdom are available. That’s 64.

Lake Kingdom:

All except 28: Taxi Flying through Lake Lamode, 29-31 - the Style Sisters moons, and 33: Peach in the Lake Kingdom are available. That’s 28.

Wooded Kingdom:

All except 52: Jammin’ in the Wooded Kingdom and 54: Peach in the Wooded Kingdom are available. That’s 52.

Cloud Kingdom:

There’s only two regular moons to begin with, and one is locked behind Peach. So only 1: Picture Match: Basically a Goomba is available.

Lost Kingdom:

All except 22: Taxi Flying through Forgotten Isle, 23: I Met a Tropical Wiggler!, and 25: Peach in the Lost Kingdom are available. That’s 22.

Metro Kingdom:

All except 52: A Tourist in the Metro Kingdom, 55: Mario Signs His Name, 56: Surprise Clown!, 57: A Request from the Mayor, 58: Jammin’ in the Metro Kingdom, 62: Hat-and-Seek: In the City, 64: Up on the Big Screen, 65: Down Inside the Big Screen, and 66: Peach in the Metro Kingdom are available. That’s 57.

Snow Kingdom:

All but 36: Hat-and-Seek in the Snow and 37: Peach in the Snow Kingdom are available. That’s 35.

Seaside Kingdom:

All but 52: Peach in the Seaside Kingdom are available. That’s 51.

Luncheon Kingdom:

All but 48: A Tourist in the Luncheon Kingdom, 51: Jammin’ in the Luncheon Kingdom, 54: Hat-and-Seek: Among the Food, and 56: Peach in the Luncheon Kingdom are available. That’s 52.

Ruined Kingdom:

All but 5: Peach in the Ruined Kingdom are available. That’s 4.

Bowser’s Kingdom:

All but 40: I Met a Pokio! and 45: Peach in Bowser’s Kingdom are available. That’s 44.

Moon Kingdom:

All but 5: Caught Hopping on the Moon!, 7: Moon Kingdom Timer Challenge 1, 17: Moon Shards on the Moon, 18: Moon Quiz: Amazing!, 21: Walking on the Moon!, 22: Moon Kingdom Regular Cup, 23: Doctor in the House, 24: Sphynx’s Hidden Vault, 25: A Tourist in the Moon Kingdom!, and 26: Peach in the Moon Kingdom are available. That’s 17.

Total:

463. That’s over half of the total moons available. While that’s more than enough to unlock Dark Side right off the bat, it’s not enough to unlock Darker Side, even accounting for multi-moons. (Multiple shopping moons aren’t available until post-game.) However, since there are 836 unique moons in the entire game, this is well over half of the total.

Please correct me if I missed any. I believe this is accurate, but especially on the Moon Kingdom it’s hard to keep track of what’s available during the first play-through and what’s available only in post-game.