Dear Stéphan,
A custom keyboard layout file you make with Ukelele will work with every keyboard, even if the layout you see in Ukelele’s window is not matching your hardware, or if some of the hardware keyboard’s keys are not shown at all.
In other words: if the editing window in Ukelele looks like your hardware keyboard, it’s nice, because that way it’s more comfortable editing the custom layout, but that’s it.
So for easy editing, you should experiment with the different Keyboard Types (I’d suggest USB Pro Keyboard) until you find one that is close to your actual hardware, but don’t worry if it’s not completely the same.
There is a way in Ukelele to edit key assignments for keys that are currently not shown, and that is by going by "keycode". If you know the keycode of a key that is not shown, you can still edit its assigned characters that way.
When you use a Windows hardware keyboard on the Mac, the Option and Command keys are usually swapped (compared to Apple keyboards). That is something you can repair in the System Preferences under Keyboard / Modifier Keys.
In theory, one can assign different characters to e.g. Left Option + K and Right Option + K, but in practice, that is better to avoid. It doesn’t work in many applications, for example.
That "droplist" key is the Windows Menu key. Unfortunately, that key doesn’t do anything when you connect the keyboard to a Mac.
Good luck!