The security of IoT devices is always being questioned, such as these discussions from CES 2021. As with any Internet-connected device, it is possible for a doorbell to be hacked. Always look at any built-in security features, such as encryption, and use a strong password to secure your own home network.
Also, if you store your videos in the cloud, then the security will depend on the security policy of the manufacturing company, which is beyond your control most of the time.
Overall, smart doorbells are just like any other connected device in your home, all with a possibility of getting hacked (or not).