I just started planting black pine seeds around late August. The seedling's cotyledons seem to be dying so I google about the seedling diseases and I found that these guys need to be exposed to sunlight to prevent fungi (or whatever, sorry I'm pure beginner). So I took one out and leave it in the sun for 30 minutes and it turns out to be even worse Dx (The Top pic).
When you start seedlings, the main goal is to give them optimal conditions, which usually means mimicking the (best case) conditions in their natural environment.
For black pines, this includes well-draining soil and not too much fertilizer. They grow in coastal areas with little to no frost.
Looking at your seedlings, I am wondering what kind of growth medium you are using? As mentioned before, a closed pot will quickly run into drainage issues and root rot unless you are very careful. I would very carefully transfer them into plant pots with holes - use a saucer or cache-pot if you like, but empty it after watering.
Many plants from coastal areas struggle with low humidity (in the air) and dry tips can be an indicator. However, I suspect sunburn: even plants that thrive in full sun need a transition phase if they spent a certain time indoors, starting with dappled shade and only slowly transitioning to full sun.
If you can (and your climate permits), keeping your pines outdoors will be the best for them in the long term. They need the seasonal change and the winter rest, which they will never get indoors.
