I believe you are referring to the Microsoft 365 Defender.
"Confirm user compromised" won't take any action on the account , however Microsoft Defender detects compromise based on actions and by confirm it, the account will mark as risk but the user still is able to access it. The "Suspend user" will take action on the account and prevent the user from login and you may do this action while you are doing investigation and want to prevent further compromise.
