Unpairing a Bluetooth device when there is no “i” [duplicate]

Workplaces and schools can prevent bluetooth modifications via an installed configuration profile. Check for the presence of such a profile at Settings > General > Profiles.

Using Apple Configurator 2 (an application made by Apple to allow companies & schools to administrate their employee's/student's devices) there is an option:

Allow Modifying Bluetooth Settings (supervised only)

Unchecking this option in the installed configuration profile will prevent iOS from forgetting the device.

Note: It is the same for Profile Manager in macOS Server

If you are using iOS with an installed configuration profile, I would suggest contacting your IT department and requesting that they allow you to edit Bluetooth settings.

Heres a picture of what it looks like in Apple Configurator 2:

I've experienced this phenomena as well, usually have restoring from a backup, and found that I had to delete the apps associated with the devices in order to make things work properly.

Delete the app associated with the bluetooth device.

This may remove the device from your iOS bluetooth devices list.