The "iPhone Unavailable" screen is not a bug and it is not bypassable — it is Apple's lockout counter, and the only exits are the ones Apple provides. Which one you use depends on whether you can still authenticate to the Apple Account.
If you know the Apple Account password (iOS 15.2+): on the Security Lockout screen, tap Erase iPhone, enter the Apple Account password, and the phone wipes itself and restarts to setup. Restore your iCloud backup afterwards. This is the fastest path and it needs no computer.
If you do not know the Apple Account password, or the phone is on an older iOS: you need recovery mode. Connect to a Mac with Finder, or a Windows PC with Apple Devices or iTunes. Force the device into recovery with the button combination for your model (on Face ID phones: press and release volume up, press and release volume down, then hold the side button until the recovery screen appears). Then choose Restore, not Update. Update exists too, but it does not clear the passcode.
After a restore: Activation Lock asks for the Apple Account that was signed in. If that is you, sign in and you are done. If it is not — a second-hand phone, or a device a family member set up — you need the original receipt and Apple Support. Activation Lock bypasses sold online are either credential harvesting or hardware hacks that break the device's security for good.
Set-up advice so this does not recur: use iCloud Backup with enough storage, keep the Apple Account recovery key somewhere you control, and add a trusted family member to your Apple Account recovery contacts. A forgotten passcode is recoverable; a forgotten Apple Account without recovery is the case that ends in a wiped phone.
One expectation to set: no app can get past a locked iPhone, and Ultimate Phone Spy does not try. It runs on Android, Windows and Mac, where you can install and administer monitoring on a device you own (system requirements).