My point is to be careful about attributing to the Bible claims that are not there. I am not challenging the logic nor the likelihood of your claim that transactions will all be electronic or digital. They are just not something, as far as I am aware, that are described in the Bible.
There are also descriptions in Revelations of horse-mounted armies. (See chapter 8.) This would be unusual using modern warfare. However, we do not know what events may lead up to the one described that could make the use of horses a reality. Or, perhaps the horses are figurative or the best way of describing futuristic technology in first-century Greek.
As far as the mark of the beast goes, it is possible that cash transactions continue but still will require the “mark” for identification purposes. So, you may be right that financial transactions during that time are cashless, or it could turn out otherwise. We do not know for sure right now.