We don't need "everyone" to use cash for "everything", just some people to use cash for some transactions.
It is legal in most jurisdictions to give discounts when paying with cash. That is enough motivation to use cash for larger purchases, since it saves costs for both the merchant and the customer. The only loser is the now-redundant payment processor.
Some merchants have influence over both revenue and cost. Some merchants understand the economic value of transaction data ("data about money is more valuable than money") and prefer to utilize their transaction data directly, instead of blindly surrendering it to random observers in the payment supply chain. Some customers, when given a choice, prefer those merchants.
The problem as stated by the topic is that those who are cashless (which is a vast & growing amount of people) are subject to having their digital assets frozen on a moment notice.
These proposals that we need to focus more on cash-ed people are mishearted & distracting from the core topic. Sure, a more cash-ready society is better able to help someone who has to rebuild their life, forced into a cash-carrying state. But it does nothing to prevent or remedy having your assets stripped from you by the whim of some megacorporation trying to improve their PR spin on a hot-topic.
People need assistance before being thrown to rock bottom by the corporation, not just after.
It is legal in most jurisdictions to give discounts when paying with cash. That is enough motivation to use cash for larger purchases, since it saves costs for both the merchant and the customer. The only loser is the now-redundant payment processor.