All data that you store is only being stored on your own private iCloud account storage. Take a look more about iCloud data protection and security. https://support.apple.com/en-us/ht202303

In this field there are a number of different Password category apps, but non of them provide only native way of storing your valuable information. Part of them use 3rd parties others just doesn't provide enough app  user friendly experience.

All iPhone, iPad and Mac version are supported and you can take advantage of having synced data between all of these devices using only one same iCloud account.