Multi-column layouts only work if there's no vertical scrolling, or at least if the layout reflows so that there's no need to keep scrolling down & up & down to read each page of content.
If it's done well, pagination is nice. But (as in my previous post) I'm reminded of PDFs of multi-column articles where the text is tiny and doesn't re-flow when zoomed so you end up zooming in on the page to be able to read it, then scrolling down to read the text that's now off the bottom of the screen, then up & over to the next column, down towards the bottom again, etc. Then finally down to the next page & back across to the first column. That is a much worse experience than just scrolling in a single direction.
It's fixable, of course, by "just" re-flowing the text to match the viewport size. On a desktop, pages of multi-column text at a readable font size are nice. On a phone, multi-column text would be annoying, but a smaller font size can be used because phones are typically held closer to the face than computer monitors. Getting the layout to work correctly like this isn't something I can actually remember ever seeing, but it'd provide a "best of both worlds" way of reading.
Columns that adapt to window height is a solved problem, if you for example check out epub.js [0] or the built in ebook reader in Yandex browser. I'd say this is a "just" problem with no particular difficulties to implement.
Continuing with scrolling as default instead of pagination after the switch to high-res wide screen monitors was a mistake by browser makers. The future of the web - I think - will be with browsers that are real user agents and open every web page in reader mode, with multi-media presented exactly as the user wants. No more letting web-sites control CSS.
As for web-apps, they are not the web, they are programs and should live as PWAs in the OS instead of as bookmarks in the browser.
Like you wrote, there is little reason for column view on phones. Their width is one column and no more. I agree with you that it's strange that we never see this, especially on blogs or newspaper websites, where column view should be used.
