Keychain sync and other issues...

iCloud Keychain is not like other cloud services. Normally, all of your data is stored on Apple's servers and any new device and pull the information from there. But iCloud Keychain does not work that way. Your passwords are not stored on Apple's servers. They are only stored on your devices.

This can be a problem when you are setting up a new device, or an old device. The devices may not be able decide which of them needs an update. I think the problem came from disabling the old phone before setting up the new one.

Here is a support document from Apple that might help: https://support.apple.com/HT203783

This kind of problem is usually easier to understand and keep resolved going forwards. Once you have a situation where devices are confused over which one needs updates, you may never get them working again.

One possible solution would be to avoid restoring from the old iPhone 11. If you just set this up as a new iPhone, it should pull all of your iCloud data, including iCloud Keychain data from the older device. But this is only going to work if you had pretty much everything iCloud turned on. For example, if you didn't have iCloud Photos enabled, then your photos are only going to be in the backup.

My recommendation would be to stop everything, go through your existing passwords and record them in a secure location. You may need to reset iCloud Keychain to get it working. It is also likely that having those phones get confused could cause you to lose those passwords.