The developer options are well hidden within the system settings of the HTC U12+ and therefore not visible from the beginning. This means that they have to be activated first to make them visible.
The developer mode offers you settings like for example the "USB Debugging".
How this works is explained in more detail in the following short manual:
Make the developer mode for HTC U12+ visible
1. Open the App menu and there the system settings of the HTC U12+
2. Scroll down to "Phone info" (Device information)
3. Now select "Software" or "Software information"
4. Here you will see the menu entry "Build number" - tap it several times in quick succession to unlock the developer options on the HTC U12+.
An info message will then appear at the bottom of the display indicating that the developer mode is now displayed in Android.
5. Now return to the menu for the settings. At the end of the list you will now see a new menu item.
You now know how to unlock and activate the "Developer Options" on the HTC U12+: