Why does only selecting one face select multiple faces occasionally? I'm very new to 3D modeling in general. I've been working on a Blender project over the past day, and recently, when I would edit one face on the right side of my model, it would select/edit another face on the left side. Also, I can't select anything on the left side at all. Can anyone explain why this is happening, and how I can fix it?
You probably made a linked Duplicat by pressing Alt + D insted of Shift+ D.

You can unlink them like here.

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