As a Unity dev of 6 years, playerPreffs (the unity system that stores data in the registry) are a good place to store small amounts of data in a dictionary style structure quickly without creating your own data system. But they are extremely limited in the types of data they can hold and the control a dev has over them. Whenever I see playerPreffs used I think the dev must-have needed something quick and easy. They may have also created their own registry save system in that case should be an easy fix. (De)Serializing json or even custom binary files in compartmented files in a defined folder like StreamingAssets gives much more flexibility in data types and control. You can see playerPreffs limitations in the documentation below: (https://docs.unity3d.com/ScriptReference/PlayerPrefs.html)

I would recommend one but I have always been wery about sending password data through the internet to be stored on some companies server. So I put in the effort to host my own Vaultwarden docker instance through TrueNas scale (True charts) on my home server and access it via a VPN tunnel (Wireguard). It’s very complicated to setup compared to a web service but this way I own all of my password data locally. The android app (Bitwarden) works alright but sometimes it has trouble understanding what is a login screen and you have to force fill things. Vaultwarden as a docker instance works great. The only time this setup needs to be on VPN is to save a new password. Using existing passwords seem to be cached on my device.