You need a chip for VGA->HDMI but they exist, and you can buy simple adapters. I think HDMI->VGA adapters might be cheaper (I have one in a draw somewhere) , One of the more tricky points with HDMI is that they are stricter on what they call a valid image and make weird assumptions like All your pixels are the same width.
A CRT can make do with signals to say "go to the next line now", "go back to the top now". and then just output whatever is coming in on the colour signal. It really means there is no concept of a display mode. It's all just in the timing of the signals on the wires. Plenty of modern hardware with digital internals look at a lot of that and just say "That's not normal so I quit".
Analog devices may make a high pitched whine and then explode, but at least they'll attempt the task they have been given.
A CRT can make do with signals to say "go to the next line now", "go back to the top now". and then just output whatever is coming in on the colour signal. It really means there is no concept of a display mode. It's all just in the timing of the signals on the wires. Plenty of modern hardware with digital internals look at a lot of that and just say "That's not normal so I quit".
Analog devices may make a high pitched whine and then explode, but at least they'll attempt the task they have been given.