Have you writing an spec compatibile HDMI/DP controller in HDL? It's insanely complex.
VGA is a walk in the park that's sane and easy to understand for beginners. You just need to modulate the 3 primary colors between 0-255 for 8 bit color, and two clock signals, and the monitor will display a picture.
VGA is also very simple to debug since as long as there's some signal on the color and clock lines, the monitor will display something allowing you visually see what's wrong, while on digital, if some part of the handshake failed, you get no picture on the monitor so there's no way to figure out what's wrong without specialized knowledge and equipment.
A CRT is basically it's own oscilloscope of the signals on the VGA cable making development a joy.
DVI is almost literally digitized VGA, with analog signals replaced by differential signalling and symbol encoding to keep it DC-balanced. HDMI extends it by encoding audio and extra metadata (eg. used colorspace) inside blanking intervals (yes, they still use blanking intervals that were originally required for CRT displays). It doesn't do any handshake. Main difficulty is just high clocks required, and necessity to dynamically pick symbols (unless you only use few preselected DC-balanced values). DisplayPort and HDMI 2.1 are different, with packet-based transmission.
HDMI 2.0 requires bidirectional communication between source and sink through SCDC registers to set parameters such as scramble_enable, clock ratio, and to read status flags such as clock detection, channel lock status, bit error rates etc.
VGA is a walk in the park that's sane and easy to understand for beginners. You just need to modulate the 3 primary colors between 0-255 for 8 bit color, and two clock signals, and the monitor will display a picture.
VGA is also very simple to debug since as long as there's some signal on the color and clock lines, the monitor will display something allowing you visually see what's wrong, while on digital, if some part of the handshake failed, you get no picture on the monitor so there's no way to figure out what's wrong without specialized knowledge and equipment.
A CRT is basically it's own oscilloscope of the signals on the VGA cable making development a joy.