For some reason, one of my sites has an issue where the Etch pages don’t act like pages in the Gutenberg editor, but all the content is squished into the post content width. I tried all the recommended ways to fix it, but nothing worked, so I added one line of CSS in the wpCodeBox targeting the Gutenberg editor.

.block-editor-block-list__layout.is-root-container > :where(:not(.alignleft):not(.alignright):not(.alignfull)) {
    max-width: 100%!important;
}