Giante granite kits . Just did my kitchen. Looks great.
Rustoleum also makes a kit.
If you’ve already painted it with a laminate painting kit, it doesn’t need sealing.
If you painted it with latex or chalk paint, it may not stay on the top. As in it will come off when cleaning it.
If that’s the case, then you’ll need a marine grade polyurethane and expect to clean it quite delicately.