I would never pay for anything with it.
I've been born and lived in EU all my life and the most common way to pay online is with credit card. Most websites do not accept much else.
Some more traditional companies do accept direct transfers.
What I would say is most unusual in Germany is the number of stores that don't take CCs, or even don't take any cards. People don't use them, but they have them.
Important to note that 80% of those are what the study calls "charge cards", which is 'credit cards' that resolve against an associated debit account. Not sure if those even allow overdrawing it. And 82% prefer paying with a debit card rather than credit if given the option, which indicates to me that this is a mere reaction to the online prevalence of credit cards which will go down as stores offer more non-credit card options. (As we can see by the slight reduction in '21.)
In other words, I believe this prevalence represents a desire to be able to interface with websites, rather than a desire for credit. People largely don't own a "credit card" so much as a "debit-VISA adapter."
Incorrect. This is Europe and direct payment is the norm.