When copying collapsed headers, it copies all the content inside

Not sure if this is intentional, but I want to collapse the headings, then send an email with a summary with just headings, but it copies all the content when the headings are collapsed.

Are you using an automation to send the email? If you have a formula (or markdown) to specify the content of an email that gets sent by an automation, the automation does not know about the current collapsed/expanded state on the UI.

It’s probably tough to solve this, since automations are ‘backend’ functionality.

No, just copying and pasting.