Whoever posted the user script that extends Mastodon's columns to full width (https://userstyles.org/styles/userjs/135501/Mastodon%20AutoResize%20Columns.user.js) thank you so much. I refreshed to see it before responding; don't remember whose post.
Octodonians, add these lines to your script if you want it to work here:
// @include https://octodon.social/*
// @include http://octodon.social/*
// @include http://*.octodon.social/*
// @include https://*.octodon.social/*