Split stem on seedling

Looks like a split hypocotyl, not classic damping-off. That can happen when seedlings grow fast in very humid conditions and the outer “skin” can’t keep up, or when the shell/cotyledons pull a bit awkwardly as they pop. As long as the stem is firm, not mushy, and not pinched at the soil line, the plant can usually heal and form a little “knuckle” there. My advice: Stop spraying the stem directly – keep the top layer just slightly moist, not wet. Take the dome sometimes / vent it more so it’s not constantly 100% RH. Add a very gentle breeze so the seedling can strengthen its stem. Optional: give it a tiny support (toothpick + loose tie) for a few days. If the split area turns brown and corky and the plant keeps growing, you’re fine. If it goes dark, slimy and the seedling flops over, that’s damping off – then there’s unfortunately not much you can do for this one. Good luck! 🙏

Should be fine. Just let it grow like your hair.