Before beginning, ensure you have:
If CATIA fails to find your license despite it being valid, you may need to manually point Windows to the right place. install catia v5 r21 on windows 11 fixed
Since R21 uses old OpenGL standards, ensure your Nvidia/AMD drivers are up to date. If the screen flickering persists, go to Tools > Options > General > Display > Performance inside CATIA and disable "Hardware Acceleration." Conclusion Before beginning, ensure you have: If CATIA fails