When playing against an opponent who is much stronger than you, it can be beneficial to choose a solid opening that avoids tactical lines and provides a steady positional game.
Some suggestions for such openings are the Slav Defense, the Caro-Kann Defense, or the French Defense. These openings aim to control the center of the board with pawns and develop your pieces logically without engaging in any aggressive tactics early on.
Another good option could be the Queen's Gambit Declined, which is a solid and reliable opening that helps to control the center of the board while avoiding potential tactical pitfalls. Regardless of what opening you choose, remember to focus on playing solidly and cautiously while looking for opportunities to develop your position.
It's important to note that openings alone cannot win games. You should focus on studying tactics, positional play, and endgame principles to improve your overall chess skills.