I just started a new job and I'm actually miserable 🫠

I just started a new job recently and I feel existential dread everyday because of it. I accepted this job offer because of how the company was sold to me and the decent raise I got by making the jump, but now that I'm here, the culture is not what I was sold on and the job isn't at all fulfilling. My supervisor has never supervised anyone before and has no experience with the work that I do (marketing), plus she's younger than me, although we sit at the same level in the org chart.

I really don't know what to do here. My mental health is spiraling and I don't know what to do. I feel so incredibly stuck and hopeless. Does anybody have advice here, aside from job searching? I'm already doing that, but I know that that can take time. I just need help.