There seems to be some confusion about two very different things;
proof of funds when getting a visa from a thai consulate (at the consulates which require it)
AND
proof of funds when entering the country (if you are unlucky enough to be asked by passport control when you stamp in).
At the consulates which require proof of funds to issue tourist visas you CANNOT use cash, you must show a bank statement, but it doesn't have to be a thai bank account.
If you are asked to show proof of funds when you stamp into the country you CANNOT use a bank statement, you must show cash, but it doesn't have to be thai baht, it can be in any currency.
Just wanted to touch on those things because they come up quite often in topics.
TLDR : Answer Summary
There is a distinction between proof of funds needed when applying for a Thai visa at consulates and when entering Thailand. For tourist visas at consulates requiring proof of funds, a bank statement (non-Thai bank accounts accepted) must be provided, while at immigration, they typically require cash in any currency. This confusion arises as both situations have different requirements.