Sign in with the Gmail account for your IG Account, don’t use your primary Gmail, and don’t enter your primary Password. BlueStacks doesn’t accept the App Password Codes from Gmail, requiring instead that you enter your complete email password into the app, which is definitely a bad idea
You can make a new Gmail account just for your IG account, or a different one for each account.
Then you can change the email linked to your IG account in your IG account settings
Log in with your alternate Email
Open Google Play Store and Install IG
In your IG Settings on your phone, you may need to disable 2-factor Authentication; I’ve never gotten IG on BlueStacks to send me the Verification Code to my phone, but that could be IG’s own internal doing, trying to prevent third-party access
You can now use IG from your desktop, just like you would on your Phone