Leggy Seedling Recovery attempt

Seedlings get leggy like that from too little light. Burying the stem was not a good move. It's much better to just support it, although like m0use said, it looks like it has had damping off start to creep in and little chance they survive that. Having the stem in the wet and dark environment is a great way to pick up issues. It's a perfect environment for fungus, so you just gave the damping off some help and that seedling will most likely die in the next few days.

don't go overboard with the light. you may have too much for a seedling now. looks like you buried a portion of leggy stem on transplant - good idea. Now all you can do is get your light right. if no stem develops between growth nodes, reduce light. it could be why the leaves are paying, which is too early to see that. the seed has enough energy to power itself the first 10-14 days. so either bad batch of soil (amendments too hot or whatever), or the light is too close. i doubt you have a quantum meter. that "40" dli is consistent but not an accurate measuremnt. Also, stick to an 18/6 schedule unless you have an underpowerd light. It's not about hours it's about DLI. it doesn't matter if you are near max DLI over 12 hours or 20. the same results will occur.