Do you use the Content & Privacy restrictions within the screen time settings? I use this on my iPhone to lock down my Apple account settings as a secondary level of protection should my iPhone be accessed by another person they will have this additional barrier before they can lock me out of my own Apple account. It does prevent changes on some settings that are not always obvious. It might be worth disabling this setting and make your change and then re-enable the setting again to restore the additional protection.I have reviewed this thread and cannot determine if the following bug has been removed in any of the betas:
Settings> Privacy & Security > Wired Accessories. You cannot change the setting from "Always Allow".
A message says the following: "This setting is managed by your organization and cannot be changed"
This is a significant security issue and will allow 3rd party chargers that are hacked to get access to your phone's content.
I am on 26.0.1 and it is a private phone that is not managed by any MDM software.
Not sure if this will have any impact on the issue but I have found a few settings that I cannot change until I remove the restriction in screen time. Worth a check?