how to get support without serial number

Thanks for the magical response!

Yes it's my phone... about 4 phones ago. So unfortunately, it's no longer in "manage" since I haven't had to manage it for a couple of years.

You're so right about the backup showing the serial number! Except the phone won't get past the apple logo and just keeps restarting itself (before your next magical reply... yes I absolutely went through all the troubleshooting recommendations to remedy this... those don't work either.

The point of this post is: how are apple customers who do not have access to a device's serial number (my situation) able to seek support when they cannot get past the "serial number" requirement in order to move along in the support process for their not so new devices? I've tried everything I can think of, searched websites, apple's site, forums, even entertaining magical responses from knowledgeable and helpful people such as yourself, but am unable to get further along the support process due to this issue. It's a flaw in Apple's service process. As a loyal Apple customer for 15 years, having purchased at least 30 apple devices and currently have 5 devices in "manage," I hope that my opinion matters enough for someone from Apple to offer me actual support for my device rather than have this bad excuse for a "help" center give advanced users obvious, yet repetitive and ineffective tips full of attitude from strangers behind a keyboard.

Thank you. This would normally be helpful. However, this is an old phone of mine I haven't used in a few years. The phone is no longer backed up to my iTunes or iCloud. It also won't turn on or update or restart or reset when connected to iTunes. I'm trying to mail it in for repair, but I need to provide the serial number before I can do that.

How can I do that when the phone won't turn on, won't connect to iTunes, and is missing the SIM card tray?

Thanks. Unfortunately, my SIM card tray is missing. I no longer have the box or receipt. and it won't turn on.

How would you suggest I find the serial number now? It's an iPhone X.