Serial window with ATtiny45/85 and library ATTinyCore

Hallo,

the target is, I would like to switch on/off an ATtiny45 over an LDR on PIN2.

To see how the LDR works I would test the serial communication with an ATtiny45. The connection to the ATtiny45 from Uno to ATtiny works and I can upload Test Sketches with LEDs on PIN 0,1,3 and 4.

For my serial connection test I use the information from this video “ATTINY-85 Serial Monitor. Step-by-step Arduino IDE Guide” https://youtu.be/9CX4i6rMXS8. All about ATtiny85 I changed in the AdruinoIDE to Tttiny45.

I have used the instructions on the end of the video and used this mentioned sketch from the author:
Tom Donnelly on YouTube: “ATTINY-85 Serial Monitor. Step-by-step Arduino IDE Guide”:

"#include <SoftwareSerial.h>

SoftwareSerial Monitor(5, 4);

void setup() {

Monitor.begin(9600);
pinMode(0, OUTPUT);
pinMode(4, OUTPUT);
pinMode(5, INPUT);
}

void loop() {
digitalWrite(0, HIGH);
Monitor.println(“LED on”);
delay(1000);
digitalWrite(0, LOW);
Monitor.println(“LED off”);
delay(1000);
}

On Adruino Uno the LED for Tx is blinking - RX is off
PIN3 (analog) is connected with RX on Uno
PIN4 (analog) is connected with TX on Uno

The message is this:

Der Sketch verwendet 2170 Bytes (52%) des Programmspeicherplatzes. Das Maximum sind 4096 Bytes.
Globale Variablen verwenden 140 Bytes (54%) des dynamischen Speichers, 116 Bytes für lokale Variablen verbleiben. Das Maximum sind 256 Bytes.
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

Who has any idea why the sketch is not upload?

Thanks for help
Mike