Featured image size

Hello, I’m coming from the Lovecraft theme where i set up featured image sized 2560x600px.

I’m testing Bjork on a local install and I’d like it to serve featured images of the articles that I’ve published in the past with the correct proportions, as I see them in the backend.

Instead, the frontend serves the 88×88 px thumbnail and the result I get is terrible. The same issue appears in the single posts.

I’ve already tried all the format settings (1:1, 16:9…) in the freatured image menu, but i can see the changes only in the backend. The frontend keeps serving the smal 88×88 thumbnails.

Could someone suggest what the solution could be? Thank you