Setting thumbnail for video not working

I'm trying to set a specific frame to be the thumbnail of my video when it's exported. I've tried so many things regarding 'setting poster frame' but it's not working. Whenever I export the video and look at it in Finder on my Macbook, it still shows the first clip of the video. I'm attaching screenshots to show my issue.

I even saw some advice about adding a thumbnail photo to a video inside Finder when clicking 'get info.' That didn't work either! Wtf.

I have Premiere Pro 2024 and a Macbook Pro 2023.

Does anyone know how to fix this?

Thank you!

Gaby