With absolutely no internal knowledge, I assume the author cuts the panels in traditional book style and specifies colors and background etc., and from there basically two teams running in parallel, one producing the vertical stream from the digital assets, and the other executing on the panel format.
This makes the vertical stream very readable, well balance and optimized, with none of the clunky artifacts that appear on manga that have been 'converted' for mobile format.
Looking at how there's actually three (!) versions of the series released in parallel, I'd assume they're just throwing money where it matters to cover the most ground.
(It's a bit like asking "how well does putting comics on pages work?" Different comics use the medium very differently.)
It's also a great manhwa, and supporting the authors and English translations can't be a wrong thing to do. :)
https://books.apple.com/us/book/solo-leveling-vol-1-comic/id...