It's not just having liquid cash. You MUST show that the money was not borrowed. That's the whole point of a 6 month average balance or bank statement. The only exception is a gift deed.Yes, it's a Fixed Deposit. It can be made anytime. It has no criteria for being six months old. It's a liquid asset which can be cashed out instantly.
There are several threads explaining the same thing. Here's one: https://www.canadavisa.com/canada-immigration-discussion-board/threads/fixed-deposit-as-proof-of-funds.394087/