It’s a pity you don’t take my advice of…
As I said before, if the hardware works with Blynk Legacy then it should work with Blynk IoT, with a few code changes. However, you’ve not shared your code (I see you say that it’s 4k+ lines long) or any other useable information other than the hardware and the version of Blynk you are using.
If you want assistance then I’d suggest that you create a bare minimum sketch which works with your hardware and Blynk legacy. After you’ve tested it then post it, along with your serial monitor output.
Then, try to elaborate on what changes you’ve tried to make to get it it working in IoT, including the steps you’ve taken regarding templates and devices in the Blynk IoT web console, and what results this shows in the serial monitor.
Unless you make some effort yourself you’re unlikely to be handed a magic bullet by the forum members.
Pete.