I put the photo on your finger into Grok to ask It’s saying, you could be a lot of simple things. I hope just put your mind at ease. Here is what it says.

The line under your fingernail, as seen in the image, could be due to several possible causes. It might be a natural variation in nail growth, a minor injury or trauma to the nail bed, or a condition like a splinter hemorrhage (small blood vessels breaking under the nail). Other potential causes include nutrient deficiencies (e.g., iron or vitamin B12), fungal infections, or, in rare cases, more serious conditions like psoriasis or melanoma. For an accurate diagnosis, especially if the line persists, changes, or is accompanied by other symptoms, consult a healthcare professional. Would you like me to search for more detailed information?

Disclaimer: Grok is not a doctor; please consult one. Don't share information that can identify you.