I don't know if theres been any recent change, but not too long ago, login is only required to view Instagram stories. Then they changed it to block location-tagged postings too. Which is a bummer, since I liked to use the webbrowser to browse location-tagged Instagram posts to discover places to eat at. I haven't used it much since, not sure if they added additional restrictions for non-signed-up users recently.

It's new, I think since last Sunday in Switzerland.

Definitely a new change, just last week I could look at user profiles without having to be logged in. Right now, it shows me an overlay asking me to log in.

I saw this behavior if accessed with a mobile user-agent. Switching to a desktop user-agent unlocked the thing.

What country are you in? Definitely never been the case in the US.

You used to be able to close the pop up login box