You need to show a whole plant picture. One leaf does not make for an unhealthy plant. If it were my plant I would gently transplant out of that MG soil and into an actual quality potting soil, though. j
Plant looks just fine. That single leaf is simply one of your oldest original leaves and it’s completely normal for it to die off. i would still transplant into a larger container of high quality soil mix soon. Go here: Automatics make good Organic sinse @Organic sinse will be the man you’ll want to talk to regarding getting the most high quality cannabis out of your Autoflower plant. j
^ what he said what you're seeing on that particular leaf looks very much like you over sprayed and left droplets on the fan leaf. Did you by chance water early in your light cycle, hit the plant with some foliar spray, and let the droplets cook under your light? When you leave water droplets on your plants under light, it acts as a magnifying glass and cooks them. If you are going to apply a foliar spray, I would recommend doing it toward the end of your light period so that when you're done the lights will be off soon.