Unknown device

Looks like it is your Windows OS PC.

See -> Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to see where you're signed in - Apple Support

See this Apple articles below:

Set up and use iCloud for Windows

Set up and use iCloud for Windows - Apple Support

Download iCloud for Windows

Download iCloud for Windows – Apple Support (UK)

Set up iCloud Passwords on your Windows computer

Set up iCloud Passwords on your Windows computer – Apple Support (UK)

Click here for more support and assistance.

OK, but if it is your Windows OS PC, don't remove it.

Additional:

Optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support