In Pokémon Scarlet, one of the hardest Legendary Pokémon to catch is Solgaleo. Here are the detailed steps to catch it:

### Steps to Catch Solgaleo in Pokémon Scarlet

1. **Complete the Main Story**:
– Ensure you have completed the main story of Pokémon Scarlet. This will unlock the necessary quests and locations for encountering Legendary Pokémon.

2. **Purchase the Indigo Disk DLC**:
– Purchase the Indigo Disk DLC, which is required to access some of the Legendary Pokémon, including Solgaleo.

3. **Access the Pokémon League Building**:
– Fly up to the Pokémon League building. This is where Solgaleo can be encountered.

4. **Encounter Solgaleo**:
– Solgaleo can only be encountered through Solo Blueberry Quests in Pokémon Scarlet. If you are playing Pokémon Violet, you will need to complete a Group Blueberry Quest to encounter it.

5. **Prepare Your Team**:
– Since Solgaleo is a Psychic-Steel-type Pokémon, it is weak to Fire, Ghost, Dark, and Ground-type moves. Ensure you have a Pokémon with one of these types to increase your chances of catching it.

6. **Use the Right Poké Ball**:
– While a Master Ball would be ideal, if you don’t have one, use a high-quality Poké Ball like a Premier Ball or a Dusk Ball. These have higher catch rates and are more effective against powerful Pokémon like Solgaleo.

7. **Battle Strategy**:
– Solgaleo uses moves like Flare Blitz, Solar Beam, Wild Charge, and Metal Burst. To catch it, you might need to weaken it first. Use moves that can lower its HP without being too risky, and then attempt to catch it with a high-quality Poké Ball.

8. **Catch Solgaleo**:
– Once you have weakened Solgaleo and have the right Poké Ball, throw it and hope for the best. If the catch is successful, you will have caught one of the hardest Legendary Pokémon in the game.

By following these steps, you should be able to catch Solgaleo in Pokémon Scarlet, despite its challenging nature.