No average Japanese person is using floppy disk technology from the 1970s. Most everybody here (I’m in Japan) is using USB flash drives, SSDs, SD cards and cloud storage just like people in ’Merica are. That article is about government organizations still using old technology systems. Which is an issue of America and any other country as well (it is not unique to Japan).
Fax machines are technically still in use, but it is not because of individual people wanting to use a fax machine or not knowing how to use more modern tech. It is more because some government and businesses still require the use of fax machines for sending documents and such (though less so every year). I worked for a Japanese company from 2011-2015 that required workers to submit certain documents monthly by fax. When I asked if I could just scan it and email it to the company, I was told their procedures weren’t setup to receive those documents by email. There was no technical reason why we couldn’t use email or another means. It was just company procedure to use fax. I would need to go down to the convenience store at least once a month to use their fax machine there. But I haven’t needed to send a fax in years now. I am sure there are a few holdout companies, but sending faxes isn’t a daily occurrence for the average person in Japan.
As for older people and new technology, there isn’t really any difficult tech associated with the My Number Card (from the user prospective). The My Numbers Card allows for people to use the card with more technology, but it isn’t a requirement.
And getting the My Number Card is just a quick trip to City/Town/Village Hall. It is possible to be in and out with the card in your hand in 10 minutes (depending on how busy they are, of course). It about as difficult as getting any other form of government ID here. Actually… getting a My Number Card was significantly less difficult (in my experience) than getting my Japanese drivers license renewed.
Renewing a Japanese drivers license… now that is an absolute pain to do, lol. It is comically-incomprehensible to get a Japanese drivers license renewed (but not because of any tech reasons… just normal bureaucracy reasons common to any country).