The VGA connection system has one set of pins as a "device present" intent. With using a DVI to VGA connector, it must pass that presence to the video card.. or there will be no signal output on that port. Very old CRT monitors did not have an ID (brand, model, type) feature, but since about 1996, all monitors did.
If your video card has two DVI ports, try the other. If still no video, then try another DVI to VGA adapter. There are different models
Then too, older CRT monitors did not have a high refresh rate.. typically lower than 80 Hz. Yet in 'basic' or BIOS mode, the video would be default VGA at 60 Hz, 640 x 480 resolution.. acceptable by almost all monitors.
Yes, there may be a "legacy" issue here too.. being not accepted as a device made before a certain date. This is also known as "abandoned" status.
F@H.. to solve mankind's maladies.. in our lifetimes!