Developer Mode on VSN Mobil V.50
Sometimes this can happen, whether it's a decision made by the vendor, or it's really an accidental mistake.

However, it doesn't mean that the whole developer option is removed from the system (though, this could really happen, as shown on the linked question). The workaround is to invoke the developer option through 3rd-party apps, such as:


Developer Options by uDroid (free)
Developer Options by SingleByte (free)
Developer Settings Shortcut (free)
and many more...


If it's still inaccessible, then the developer option might be really removed from the ROM, and you should contact the vendor regarding this.