at PC Startup I'm getting a pop-up asking to download cc.png?

I uninstalled Creative Cloud via the CleanerTool and it solved the the problem.

Not sure if I can be bothered re-installing it. Now's probably a good time to cancel my subscription. I don't really use Lightroom enough anymore to warrant putting up with and spending time trying to resolve this sort of annoyance.

Checking the domain, this looks legit. https://who.is/whois/adobeoobe.com

See here: https://community.adobe.com/t5/download-install-discussions/what-is-it-cc-png/m-p/10983379#M79300

See also here for Adobe's network endpoints: https://helpx.adobe.com/enterprise/kb/network-endpoints.html

I suppose that PNG should only guarantee that access to certain Adobe Systems are guaranteed. Did you modify your system setting recently?