Yes, if your country of citizenship is short-listed for visa exemption. It was extended to 45 days to take care of quarantine but is now back to 30 days.
Many Thai banks suspend the account when no activity for more than one year. It does not disappear but is a little troublesome to reactivate and usually not possible without showing up at the bank. To keep it active, you just need to transfer 100 THB or something in or out within every year.
You must/should ask for a bank statement for 3 or 12 months, depending on which visa you are extending? If more than 6 months, it will most likely take a week or more for the bank to avail it.