Spanish banks no longer lend based only on good savings.
If you don’t have an income that shows on tax returns, you will not be able to get a mortgage from banks and other lenders in Spain (unless you earn in UAE where there are no income taxes). Having the money in the bank to cover future mortgage payments alone will not be enough to gain approval.
No income verification mortgages were popular before the global financial crash of 2008. They no longer exist in Spain.