How can I tell if someone blocked me on Instagram? Their profile just vanished.

Instagram never tells you, so you're reading signs. Blocked: you can't find their profile from your account, but a friend's account CAN find it, that's the key test. If their profile exists for others but not you, you're blocked. Deactivated or deleted: the account is gone for EVERYONE, including your friends. So: exists for others but not you = blocked. Gone for everyone = they deactivated.

The friend test is the only reliable one. Have someone else search the username. If they see it and you don't, you're blocked. If nobody can find it, they just deactivated.

Also check old DMs, if you were blocked their messages stay but their profile photo goes blank and you can't open their profile from the chat. Another tell.