While it's impossible to find out how many people who did that, you can get rough estimation how many bitcoin was held for at least 5 years by open blockchain explorer (such as Blockchair) and filter for any UTXO with age older than 5 years.
True. Though the rough estimation would probably a little bit too "rough" and inaccurate for us to end up with data that's decently meaningful. It's pretty could potentially be as inaccurate as saying that funds from a certain wallet address is "lost" just because the funds didn't move for years.