Magento 2 Show/Hide block based on cookie – Full Page Cache issue

I am trying to show or hide a block based on a cookie. The cookie is set on a form submission and whether the user sees the block depends on if they have the cookie set.
I have it working but when Full Page Cache is enabled it ignores the cookie and just shows whatever is in the cache.

At it’s most basic I have the following at the top of the block phtml:

if(!$allowedToView){
    return;
}

// else show the block content.

I don’t want to use cacheable=false for obviously reasons.

I have considered using private content to “Hole punch” but I don’t need to display personal content, just the block itself.
Any suggestions on how best to achieve this?

Thanks.