If I think of basically anything technical I get an image in my head. Any algorithm I write first exists in my head as a visualization of what I want to do. If I can't visualize what is going on I can't understand it and am in a state of confusion.
But I don't feel like I am impacted in imagining simple algorithms. I also construct them of very simple forms and rearrange them in my mind. I also feel like it is a lot easier for me to imagine things „automatically“ due to it being memories or being a byproduct of thinking about something. But my mind struggles constructing these images at will.
Also taking a pen and drawing these things up can replace some of the missing imaginary power :)
This matches my experience - I think of it a bit like a really slow CRT, the phosphorescence fading before the image can be composed.