I am a new user and I just downloaded the windows version of Quartus Prime 21.4.
The issue I have is that I want to work on an EP4CE10F17C8N but the only device files on the download page are those of Cyclone 10GX. Is it that intel discontinued support for Cyclone 4 devices? If not where can I get the .qdz file.
Quartus version 21.4? You must have downloaded the licensed 'Pro' version. It does not support Cyclone IV.
Use the free Quartus 'Lite' version 21.1 for Cyclone IV support (or the 'Standard' licensed version 21.1 works also):
Please check the supported device section in the below link and choose the version of Quartus accordingly: