SoftwareSerial / IDE

Hello everybody:
I need another UART in the NANO 33 IOT but when I include the library (SoftwareSerial.h) and compile the Web IDE write this message: /home/builder/opt/libraries/latest/dabble_1_5_2/src/SoftwareSerial.cpp:45:10: fatal error: util/delay_basic.h: No such file or directory
#include <util/delay_basic.h>
What is wrong? I must include <util/delay_basic.h>?
Another problem is the IDE 1.8.15 (Installed in my Mac) when i try to compile any type of sketch the compilers answers with:

Arduino:1.8.15 (Mac OS X), Scheda:"Arduino NANO 33 IoT"
Errore:
/Library/Arduino15/packages/arduino/tools/arm-none-eabi-gcc/7-2017q4/bin/arm-none-eabi-g++: no such file or directory
Errore durante la compilazione per la scheda Arduino NANO 33 IoT.
Thank you very much.

How many Serial interfaces do you require and which are you currently using ?

Two. One for program and debugger (on USB) and one from a water heater

Why not use the Serial1 interface on pins 0 and 1 for the water heater which leaves the USB interface to the Serial monitor for debugging ?

I'm trying to use the Serial1 on pins 0 and 1 for the water heater but it doesen't work. If I try with the Mega 2560 it's work perfectly!! The sketch is the same like the hardware, a little different is the vcc on 2560 5V on Nano 3.3V but there are two different resistence anda i have two hardware e two optocoupler.

Is the heater connected to pins 0 and 1 on the Mega when it is working?

Are you using SoftwareSerial on the Mega?

No on the Mega I use the pins 14 and 15. The Serial number 3.
No on Mega I use hardware UART.

What exactly doesn't work and how do you know ?

The obvious things to check are the wiring and the baud rate

The concept is that: On the water heater there is a UART (RS-232), I use only the TX. The signal si hight level +/-12V to match this voltage with ARDUINO i use a a Zener, a capacitor, diode led and a optocoupler. (little circuit). The transistor of the optocoupler is connect with the Collector to the RX pin of ARDUINO and the Resistors 4.7K to +5v; the emitter to GND. I made two circuits one for Mega and one for Nano 33 Iot. Now I write a sketch that listens what arrive from UART (3 for the Mega, 1 for Nano) and write the correct data on Serial Monitor. When the Nano is running I don't read nothing on the serial monitor like it waiting the data from serial. The baud rate is 1200 and wiring is simple...
Now I think that the UART 1 of the NANO is damage..
With Mega as soon as i connect power it start to push data on serial monitor without problem. (The Mega is very strong!)

The Mega is a 5V device and the Nano 33 IOT is a 3V3 device. Have you taken that into account ?

Yess