Unfortunately that didn’t seem to work. I even tried to make it more specific and it still isn’t coming up when I inspect element.
.single-post.content-max-width .wp-block-columns, .single-post.content-max-width .wp-block-text-columns, .single-post .wp-block-columns, .single-post .wp-block-text-columns {
max-width: 850px !important;
}