Sidebar region doesn't go anywhere when empty in Olivero

Drupal core website, version 10.1.6
Theme is Olivero.

Sidebar region doesn't disappear, doesn't go anywhere when it's empty in Olivero.

I can remove all blocks from the Sidebar region and then check a webpage I would see a blank White and an empty sidebar.

I also tried to remove the Sidebar region in the hompage node with the famous module Context, but got the exact same result.

The content aside from the sidebar just won't cover the empty Sidebar area (when it's indeed empty).

What causes this problem and how to solve it?