A bank account statement about the amount on your debit account is a standard document that must be provided to apply for a visa. The amount that must be in the account depends on the living wage. From January 1, 2023, it is CZK 3,130.
If you are coming for an annual preparatory course, you should have the equivalent of CZK 115,810 on your account, which is about 4,900 euros (as of May, 25, 2023).
This money is not frozen there – you can safely use it for a year, but remember that in a year, by the time of visa extension, the amount should again be in the account. And it will again need to be calculated according to the living wage, which is updated every year in April.