Check if you can still view their profile and posts
Search for their account name in Instagram; see if it appears in results
Try to send them a message; if your chat won’t go through or disappears, it may indicate a block
Check whether your messages show as delivered or if they fail to send
Look for a shared chat; if you can’t find the person there anymore, it may indicate a block
See if you can view their story highlights and current stories
Check if their story viewer list shows your username
See if you can like or comment on their posts; missing interactions may indicate a block
Look for changes in follower/following lists (you may not be able to view them)
Confirm by having another account try to view their profile and stories
Assume it’s a block if multiple signs prevent you from viewing their content and messaging consistently