Here's how my little plant is doing on day 3 in soil, what do you recommend? Honestly, it looks a bit yellow

The cotyledon leaves look stuck so it’s not photosynthesizing

I would say so too.

Cotyledons are still stuck together.
The plant is stretching a lot (becoming leggy). A sign that it is looking for more light.

Is it a photoperiod or an auto?

For the former, the season would already be a bit too late for outdoors.