Talking about where BTC are been held, it's mostly in wallets I mean people's wallets and sometimes that of institutions,
This is not completely correct. In simpler terms, Bitcoins are stored on the blockchain and the amounts owned by the private key is assigned in the public ledger.
Your private key is what you need to access those coins from the public ledger. That is why you should never share your private key with anybody. Even if you wallet software is uninstalled, you never lose access to your coins, just install it in another device and plug in your key to regain the dashboard.
Make this topics clear beforehand because you might get caught down the rabbit hole sometime in future.