Craft Admin assets do not load over https (Apache & Cloudflare)
The solution I came to was creating an Origin Certificate on Cloudflare, installing on it on my VPS, and setting the SSL setting to Full Strict. Now admin assets are loading perfectly over https. No .htaccess or Patrol plugin required.

If someone knows more about why this worked and the previous approach didn't I would love to hear your thoughts. Thanks @MattStein for clueing me towards this approach.