For reference, this is the exact URL that doesn't work, right?
https://getsupport.apple.com
An iOS or iPadOS device would be the most reliable way to test this, one that doesn't have a management profile in Settings > General > Profile installed, and doesn't have extra certificates with toggle controls like this in Settings > General > About > Certificate Trust Settings. (A VPN can't cause this even if you have it, as a VPN can't properly man-in-the-middle an HTTPS connection.) If your iPhone doesn't have such a profile or certificate installed and it still displays 403, then I think this might be a problem on Apple's (or their CDN, Akamai's) end, as unlikely as that sounds. It's not happening to most people of course, but it may be that the specific node that you're connecting to, which is supposed to serve that page, is not working.
I'd try a different Internet connection like cellular, or waiting a few hours and see if it's fixed then.