This story from the Mail is total and utter scaremongering bollocks.
Yes, under the Schengen area rules, member states can specify that non-EU citizens prove that they have the resources to support their stay. For Spain this is about €120 per person per day.
But checking this is a total pain. It is only ever applied at Spanish consulates for people who need visas to visit Spain. If you want to go to Madrid for a month from Bangladesh, they want to see evidence that you have a couple of thousand Euros available. You have to provide bank statements. If you plan to stay with a relative who lives in Spain, that relative has to get a letter of invitation signed by the local police, which you submit with your application.(*)
This requirement is never, ever, ever, ever checked for nationals of any Schengen visa-waiver countries. There are 60 or so of those, including the UK.
Think about it, how's it going to work? Every person would have to go to a desk (whereas most people go to an e-gate). The officer would need to you to open your entire online banking. You might have to bring up the cash ISA that you've got with another bank. It would take 10 or 15 minutes per family.
Since Brexit, Brits have made over 100 million trips to Spain. And not a single one has ever been asked for proof of resources in this way. How do I know? Because that person would be all over the tabloids. "New EU lunacy PUNISHES hard-working Brit family for Brexit with CRAZY money requirement", etc etc.
Spain is not a police state. Nor is it in the business of making it difficult for tourists to come and spend their money. Indeed, during Covid, Spain bent a semi-formal EU agreement about vaccine requirements to breaking point so as not to lose too many UK visitors. They greatly pissed off Greece and Portugal in the process, as wall as Brussels. The same government is not about to start deporting bona fide holidaymakers with voucher for all-inclusive stays at 4* hotels because they don't have £6,000 in spending money on them.
Sadly the extremely (and I mean, homeopathically) theoretical possibility of such checks (based on the most literal reading possible of Regulation (EU) 2016/399, aka the Schengen Borders Code) enables the clickbait media to wheel out this scare story year after year. And because going to another country is a stressful prospect for many people, some get anxious about this, and waste time and energy on what is, again, total and utter scaremongering bollocks.
(*) Guess what? The UK clickbait media regularly wheels out scare stories about this too, suggesting that Brits need a letter of invitation for a long weekend visit to their uncle who retired to Malaga.