Just looks like signal degradation. I would still point at the cable, or a dirty VGA jack. Make sure you're set to 60Hz on this particular video card. Barring that the card could be old and tired, component-wise.

Might be worth trying some contact cleaner on the VGA port of the graphics card, it does look like a poor connection. Out of interest what video card is that?

I'm not really an expert, but I've got a couple of things you could check.

Is the resolution and refresh rate the same on the laptop and desktop?
Pushing a higher resolution, bit depth and or refresh rate requires more bandwidth. The higher you go, the more the quality of cable and its shielding matters. Or maybe the monitor itself doesn't like the resolution/refresh rate you used.

You may also get better help if you name the type of monitor and video card you are using.

Bit depth has nothing to do with this, but otherwise reducing refresh rate and/or resolution can help.
The whole system (the monitor, the card, and the cable, including connectors along the way) must be able to support the required bandwith.

The ghosting is definitely a sign of impedance mismatch, and it could be just connector having a bad connection.
If both PCs are using the same resolution, and other has crystal clear picture, then the other PC has the issue (VGA card is not necessarily broken or going to break, it may just be it was never designed to be connected to high end monitors at high resolutions even if it is capable of it).

Thanks for your help everyone 😁

To my surprise it was actually the cable. Even though I tried a different computer and the screen looked fine, I was recommended (by Harekiet and his experience with absurdly long VGA cables on a ship) to try a different cable anyway. And that actually solved it. I'm thinking that the other computer probably looked fine because it was using a different mode. Like Jepael mentioned the lower the resolution/refresh rate, the less the problem was visible.

I didn't mention the video card name because... I'm not sure. I put this together a long time ago and lost the specs document! The monitor was a LaCie Electron Blue III in case anyone was wondering.

Jepael wrote:

Bit depth has nothing to do with this

You learn something new every day 😊

Good that you got it sorted dada. Bad cables and switch boxes have been responsible for so much grief over the years. They have a lot to answer for 🤣

Great monitor to by the way, I've got the IV. Awesome mitsubishi tubes in them.