My butter lettuce seedlings have seen better days... 😅

Yeah the one on the left side is flipping you off

A good rule of thumb is perlite encourages drainage, and vermiculite encourages moisture retention.

I notice that many nurseries use perlite because they have someone who's literal job is to water those seedlings, so the soil is kept consistently wet. For me however, between balancing job, garden, and life, the seedlings tend to get neglected, and so I need them to be able to handle a missed watering or two. You do then have to be careful not to over water with the vermiculite, I've had issues with dampening off and root rot.

This year I tried sprouting seedlings in a proper grow tent with a real grow light. I did butter lettuce, even. One thing I noticed was that my spouts had almost no stalks at all. I think the stalks get long when they are trying to reach more light, not by getting closer to the light source but just by getting up off the ground out of the shadows. It was the first thing I thought of when I saw these - they look leggy. You might try getting them more direct light.