Why stars cannot touch, even at a corner
Star Battle asks for one star in every row, column, and region. It also asks that no two stars touch — not side by side, not above or below, and not at a corner.
A corner counts because those two cells share a point. If stars could sit on a diagonal, a 2×2 block could hold two of them, and the board would stop being a placement puzzle with one answer. The eight neighbours of a star are all forbidden.
As soon as you place a star, mark those eight neighbours as dots. Auto-dot neighbours does that for you. That is a help, not a rule. The rule is the same on 6×6 and 8×8: one star, and space around it.