If security comes with dependence on anyone, any party, any company to provide that security to you, and you can not control it with your practice, I see it is no longer secure but in fact it turns to be risky.

You can store your bitcoins on centralized exchanges and think they have their big companies with security resources so their platforms are more secure than your own computer, laptop, phone or wallets. It's dangerous as their exchanges can be hacked and it's not strange if a centralized exchange has hacks in its history. When hacks happen, your fund can be lost forever and without compensation from that exchange.

It's not secure if you have a vision for the future while security of your bitcoin only can come from open source, non custodial wallets and cold storage methods. You can do this, control this by yourself in very secure ways.