professional manga artists in Japan making their manga?

Some do, but software and digital methods have been adopted by many (just as in the US) due to the increased speed and greater flexibility of the digital software methods (and it's considerably cheaper). Quite a few of American comic writers have had their handwriting digitally converted to digital fonts even.

A lot of new comic artists or hobbyists will use the old paper methods but if once they start going professional and work with established companies they're going to have a lot of pressure to adopt digital methods. If you're starting out, I strongly suggest you try to learn to work digitally. It's cheaper than constantly buying supplies, faster, you can correct mistakes easier (Undo!) and you'll be able to produce your comics in a lot less time.




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