Have you noticed a small gap between the display and the body of your Google Pixel 5? Well, some early units are suffering from such an issue, and it is affected both the Sorta Sage and Just Black versions.
https://www.notebookcheck.net/Some-early-Google-Pixel-5-units-are-exhibiting-quality-control-issues.498709.0.html
I don't have this issue but I do have a bump on the back of my sorta-sage pixel 5. Looks like something got caught under the color coat. Then it looks like something rubber at it a lot.