Hi
Here is the analysis of what is happening to your plant:
1. Diagnosis: “Damping Off”
Your seedling is probably suffering from what is called damping off. If you look closely at the base of the stem at ground level, it appears to have thinned, browned and eventually bent.
The cause: It is a fungus or bacteria that thrives in an environment that is too humid and with too little air circulation.
Condition of the leaves: They are still green, which shows that the plant was trying to grow, but the "piping" at the base of the stem has been severed by rot.
2. Why did this happen?
Overwatering: This is mistake #1. If the soil remains soggy for too long, the roots and base of the stem will suffocate.
Stagnant humidity: If you used a humidity dome without ever opening it, the stale air encouraged the growth of fungus.
Stem too frail: Your plant seems to be a little “stemmed” (it is long and thin), which makes it even more vulnerable to weight as soon as the base becomes fragile.
3. Can we save her?
Honestly, once the stem has "melted" and bent like that at the base, the chances of survival are very low. The plant can no longer bring up water and nutrients.
4. My advice for the “next” seed
Less water: Water only when the soil is dry on the surface. For a seedling, a few sprays are often enough.
Ventilation: As soon as the plant emerges from the ground, a light blow from a fan (not directly on it, but in the room) strengthens the stem.
Cleanliness: Make sure your pots are well disinfected before starting again.
It's a beginner's classic, we've all almost been there caused by excess humidity at the base of the stem. Don't be discouraged, that's how you learn the "feeling" of watering!
I wish you a good evening