Is cash required to prove the 20,000 baht financial requirement for the Visa 2 + 1 in Thailand?

There are two times you're likely to be asked for proof of funds. They are treated totally differently

You can be asked for proof of 20K baht or the equivalent when you apply for a tourist visa at some thai consulates <- in this case you show a BANK account, you CANNOT show cash.

You can be asked for proof of 20K baht or the equivalent when you stamp in to the country at passport control <- in this case you show CASH and you CANNOT show banked money.