ISO keyboard keeps being mistaken as ANSI

I recently purchased a third-party Dell keyboard (Dell KB216 USB). It has the standard European ISO layout, with the upside down L-shaped 'return' key. However, every time I go to System Preferences > Keyboard > Change Keyboard Type and select ISO, it continues to treat my keyboard as an ANSI, with incorrect mapping.

After browsing forums a while, I tried deleting the file 'com.apple.keyboardtype.plist' from Library > Preferences, which forces the keyboard setup to start fresh after a full restart.

However, this didn't solve the problem, and every time I select "ISO (European)" it still treats my keyboard like an ANSI. When I go to System Preferences > Keyboard > Input Sources, it even still shows an image of the ANSI layout – no matter which region or language I select.

I'm on High Sierra 10.13.6

Any help or advice would be appreciated.