I suspect that countries like El Salvador might accept Bitcoin for such proof. How is the situation in your own country? My country will not accept Bitcoin because the government is anti-crypto.
Of course bitcoin should be able to serve as proof of fund in countries where bitcoin is seen and accepted as a legal tender or an approved legal means of making payments by its government, since we can also download and request for a bitcoin statement of account, there is nothing stopping it form being used in the same way we have been using fiat as a proof of account statement.