Illegal would by a hyperbole. But the noose is tightening a bit.
There are upcoming limits for cash transactions (10K, countries can opt to go lower), and strong requirements for identity verification at 3K or more euros in cash.
Also illegal in Denmark. You need a NemKonto by law. Also making cash payments over 15000 is illegal since 2024.
So you can't make a large purchase without a bank transfer.
Not illegal per se in Germany but you won't find a legal job that doesn't require you to have a bank account. Benefits will also only be paid electronically (exceptions for some asylum seekers apply).
You also cannot get a tax refund or pay taxes without a bank account.
Not sure how it works in countries that didn't go through 80 years of socialism, but I assume that you're saying that in those countries, your salary is required to go to your bank account and can't be paid in cash. Then you can still pretty much "stick to cash" by withdrawing the whole thing on your payday. But then idk, maybe everyone in those countries is aware of the risks related to keeping their money in a bank, it's just the internet banking that introduces the new ones for them.
Pretty much illegal in some parts of EU