Paying the interest on the debt is no problem as long as we can create new money with a keystroke.

The problem happens when the general public figures the ruse out and start anticipating and frontrunning it. Becoming a self reinforcing parabolic cycle.

Money printing is only one aspect of hyperinflation. Almost impossible to print money fast enough to hyperinflate. The real problem is as you say, the loss of confidence in the money to hold value. It is when the public would rather hold almost anything else other than money to maintain value or purchasing power. The currency essentially becomes a "hot potato".