Ok. Thank you.
As far as I understand, the operations I want to do with the timer are
It is wrong to use it inside "void ARDUINO_ISR_ATTR onTimer(){ } ". I have to use it inside the "loop". Otherwise, when my operations are delayed a little, I get the error "Guru Meditation Error: Core 1 panic'ed ...

I am using the sample code in link:
https://espressif-docs.readthedocs-hosted.com/projects/arduino-esp32/en/latest/api/timer.html
my platform Arduino 2.2.1
my Board library : Esp32 by Espressif systems 2.0.11
And I get erros for examle :
C:\Users\leno\AppData\Local\Temp\.arduinoIDE-unsaved2023118 ...