If one axis is fixed, and it is in the case of grid lanes (it's not a fully pannable infinite canvas like Figma after all), you just keep reading the content that's on the current screen, then you scroll. I really don't see how it's any different to, for example as I mentioned previously, a long newspaper with many pages; each "page" is one "screen" worth, analogously. It's like infinite scroll, either vertically or horizontally, where instead of just one item in the list, you have a few. And if we're being really pedantic, Figma users do perfectly fine keeping the context of the content in their minds even in an infinitely pannable canvas. And also, generally newspaper readers do not do what you say, scanning column by column, they instead glance their eyes over all of the headlines then pick which one looks good then they read the article attached to that, it is a free form process.

So again, I will contend that this is not a problem for the average reader. I really cannot see where the difficulty you seem to say lies.