I'm not sure if this is necessarily true. The book Reader, Come Home by Maryanne Wolf actually discusses this. There are quantifiable differences between reading online and reading physically. So much so that even printing out the same journal article can change it. It was an interesting read, to say the least.

I find I retain information a lot better if it's printed, and a lot of memory research supports this as well. It is a lot easier to picture a page in a physical book than even a page deliminated format like PDF.

Agreed, completely. I feel the same when hand writing something as opposed to typing as well, which is why I try to encourage my students to write and not just take pictures on their phones or type it in their phone/computer notepad

Watching YouTube. All 995 of them are watching YouTube.