If you spent so much time at the workplace like the Japanese you end up with a low producivity on paper pretty much by definition, because it's simply output divided by amount of time worked.
But I wouldn't overestimate the importance of computerization on productivity which is actually extremely low. Here in Germany we have a similar paper culture (although not quite as extreme) but very high labour productivity. The Japanese could simply go home or work a day less and their productivity would go up, it's not really comparable to much of Italy. (except the north of italy which is actually also extremely productive).
In fact Microsoft in Japan actually did just that and introduced a 4 day week a while ago, and productivity went up 40% (https://www.npr.org/2019/11/04/776163853/microsoft-japan-say...)