If you want to view Instagram account posts or stories without logging in, you can use free private Instagram Viewers like Dumpor, Imginn, Inflact, etc.

If you're blocked by an Instagram account but still want to track its activity, use AximoBot - a social network & RSS forwarder for Telegram.

To see who unfollowed you on Instagram, download your data on different instances and compare follower lists using tools like Nonfollowers.