Honestly, maybe the real question is: should you even be trying to view these stories anonymously? Instagram gives people control over who sees their content for a reason—if someone doesn’t want their story publicly available, it feels wrong to look for ways around that.
As for the technical side, some stories simply aren’t viewable by third-party tools because they’re restricted to close friends, private accounts, or have privacy settings these viewers can’t bypass. This is intentional and a way Instagram protects user privacy.
Maybe consider respecting those boundaries—if someone wanted everyone to see their content, they wouldn’t post it privately.