How to beat the Bug-type Gym in Pokémon Scarlet and Violet?

Pokémon Scarlet and Violet has three main storylines, and you can do any of them anytime. Each of their objectives can be done in any order, but the difficulty doesn't change because each task is at a fixed level, like the Gym Leaders in the Victory Road storyline, for example, so they have an order from lowest to highest difficulty. Katy is the one with the Pokémon at the lowest level, considering that hers is canonically one of the first gyms everyone visits since it is one of the closest to the starting point.

How to reach the Bug-type Gym?

The Bug-type Gym is in Cortondo, the town directly west of Mesagoza; there are no obstacles or anything blocking your path.

Doing the Gym Test

The Cortondo Gym Test requires navigating a small labyrinth and pushing a giant olive into a basket. You can battle trainers to open a shortcut blocked by Smolivs. If you use your Miraidon/Koraidon to jump, you might be able to push the olive over some barriers. Once the olive is in the basket, the challenge is complete.

You can do this test again at any point in the game for extra rewards, such as ingredients and a tablecloth if you complete it in under two and a half minutes.

Battling the Gym Leader

First Battle

Katy specializes in Bug-type Pokémon, weak to Fire, Flying, and Rock-type moves, and Resistant to Grass, Ground, and Fighting-type moves; there are a few bird Pokémon near the town in case you lack one.

Katy's team comprises Nimble (Lv.14), Tarountula (Lv.14), and a Teddiursa (Lv.15) that she Terastalizes into Bug-type; none has a secondary type so you can use any of the three weaknesses to defeat all of them.

After the Battle, you'll receive a TM021 (Pounce).

Rematch

On the Rematch after the game credits, she will have a Lokix (Lv. 65), Forretress (Lv. 65), Spidops (Lv. 65), Heracross (Lv. 65), and an Ursaring (Lv. 66) that she Terastalizes into bug-type.

Lokix, the evolution of Nimble, is now Bug/Dark-type, which makes it weak to Bug and Fairy-type moves in addition to its original weaknesses. However, it gains resistance to Ghost and Dark-type moves and is immune to Psychic moves. The Fighting-type resistance is lost, and it now receives neutral damage.

Forretress is a Bug/Steel-type Pokemon that is weak only to Fire-type moves. It resists Bug, Dragon, Fairy, Grass, Ice, Normal, Psychic, and Steel-type moves and is immune to Poison-type moves. Any other types do neutral damage.

Heracross, being Bug/Fighting-type, is the weakest against Flying-type moves; it is also weak to Fire, Fairy, and Psychic-type moves, keeping the same resistances as Bug-type while gaining resistance to bug and Dark-type moves.