It's annoying, but to be fair, there's a pretty visible 'let me read it first' button. Not so bad.

    substack.com##body:style(overflow-y: auto !important)
    substack.com##.subscribe-dialog-above-the-fold
    substack.com##.subscribe-dialog-sticky-modal
    substack.com##.subscribe-dialog-sticky-modal-scroll-capture
    substack.com##.intro-popup
    substack.com##+js(aeld, /scroll/)
    substack.com##+js(rc, show-intro-popup|has-intro-popup, html, stay)

Done.

Firefox Reader View came in handy here; I actually prefer its formatting too.