Read a little further.
If you don't have an iPhone or iPad, but your child does and they're between the ages of 13-17* [they are not supposed to use one below the age of 13 and you're not supposed to put parental controls on an adult because it's creepy, but they don't check], you can use their device to set and manage their Screen Time settings and parental controls.
1. Open the Settings app, scroll down, then tap Screen Time.
2. Tap App & Website Activity, then tap Turn On App & Website Activity. This allows you to see a summary of your child's device usage.
iPhone screen showing the setting to turn on App & Website Activity on a child's device.
3. Scroll down, then tap Lock Screen Time Settings.
4. Enter a 4-digit passcode, then enter it again to confirm.
[...]
After you turn on Screen Time and create a passcode to keep the settings in place, you can add parental controls to help keep your child's device usage safe, private, and age appropriate.
No separate account or device (does not require the child to even have an Apple account associated with their device), locked with a separate thing you keep from your child so you control it and they don't. You would have found this if you had looked because that's been in IOS for fifteen years. There are other ways you can use linked accounts, but you don't have to. You keep inventing restrictions that don't exist to back up your demands.
"Read my post again, check my posting history if you must"
I have read many posts from you on this subject and debated you numerous times. Whenever suggestions come up, you defend them, often in a contradictory manner. You extol benefits that don't exist, tell me not to worry about a law that doesn't ID check before jumping to defend another one that does. If you always defend things that put limits on my devices so you can have what you want without doing any work, I'm going to assume you actually like those things. If you don't, maybe try only supporting the things that don't do that, because that's what I have a problem with. If you can come up with better software that doesn't get forced on everybody, I'll likely support it. But if we just disagree, which I think we do so far, I will hold you to not misstating what exists when you describe why it's not enough for you.