On-chain analysis leaves big room for mistakes. Don't take anything glassnode posts for granted, because there might be conflict of interest, and no way of proving their statements otherwise.
leaving less than 22% of all mined BTC moving around and exchanging hands.
That doesn't mean 22% of the circulation is at custodial exchanges, though. It just means that the 78% is held untouched (not necessarily cold storage either). A fraction of that 22% is likely to be stored at exchanges.