how to fix directx 9.0 or higher error

This helped me. Startoptions (Rightclick on C&C in SteamLibary - Properties - Startoption): -win . The game started in windowed mode...

First start of the game creates a Profile under "C:\Users\xxxxxx\AppData\Roaming\Command & Conquer 3 Tiberium Wars\Profiles... ". Here i found the Option.ini. i opened it with a Texteditor, searched for Resolution and set it the Same as my Screenresolution. Before 800 600 , now 1920 1080.

Last step, startoptions again. Before -win now -win -fullscreen -xpos 0 -ypos 0 can be copied from here.

Addition: with Mods Startoptionen: -ui -win -fullscreen -xpos 0 -ypos 0