pearID is pearOS's own account system (like an Apple ID), backed by account.pearos.xyz. Logging in with it from the AppStore/Welcome flow does three things:

Your login session is stored securely - through your Linux keyring (GNOME Keyring/Secret Service) if one is available, or otherwise in ~/.pearid_token with strict 600 permissions (readable only by you).

Before wiping or reinstalling pearOS, sign out of pearID first (AppStore → Account → Sign Out). This removes the device from your account cleanly; skipping it can leave a stale device entry behind since the hardware-based device ID stays the same across reinstalls on the same machine.

If login fails, double check email/password - a 401 means the server rejected the credentials, not a local bug.