What is happening to my seedlings ?

Hello,

A few weeks ago, I have sown a few seeds of clary sage in a pot, indoor. About a week ago, three seeds sprouted, but something seemed to have cut the seedling, without even eating any part of the plant. I've done a few research, the problem could be cryptogamic or from cutworms; what do you think happened, what should I do to protect my seedlings ?

Here's a photo of one of the seedlings :

That's unfortunate. I remember having the same thing happen to my seedlings. I don't know what it is.
I can only say that probably some will survive, they might just be the healthiest ones with the best genes for your soil type/climate. Save the hundreds of seeds of the winners and sow those.

that looks more like damping off than some sort of critter damage. better airflow/a fan can help protect against it.

I have to agree that looks like damping off.  Seedlings like humidity and moisture and warmth but there has to be air circulation.  Damping off occurs when the moisture/humidity raises to a level where the little seedling can’t breath and it literally smothers. ( non scientific explanation)

That is why air circulation is greenhouses is so important.

Seedlings need to be moist but not wet or soggy wnd they need to be warm not cool or chilly.

Increase air circulation and improve warmth if necessary with a seedling mat,  I use a pet warming mat under my seed trays snd a fan in my Grow room.

Yes, damping off. Not critters.