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.
Unfortunately, in my country, if you present bitcoin as proof of funds, you will have more problems than you will be able to handle. Our governments frown out bitcoin and have no stable policy about it and have been on steady crackdown on users of bitcoin and other crypto. However, this does not deter people from buying and holding bitcoin, instead it created greater publicity and interest among the younger people. So, to avoid playing into the hands of the authorities, it is not advisable to present bitcoin as a proof of funds as that may complicate things so greatly. I think it is only in few countries that it is possible to use bitcoin as a proof of funds.