I tried again and now I've got a different error message:
Sketch uses 5130 bytes (15%) of program storage space. Maximum is 32384 bytes.
Global variables use 267 bytes (13%) of dynamic memory, leaving 1781 bytes for local variables. Maximum is 2048 bytes.
"C:\Users\nptdns\AppData\Local\Arduino15\packages\MiniCore\tools\avrdude\8.0-arduino.1/bin/avrdude" "-CC:\Users\nptdns\AppData\Local\Arduino15\packages\MiniCore\tools\avrdude\8.0-arduino.1/etc/avrdude.conf" -v -V -patmega328p -curclock -PCOM3 -b115200 -D -xnometadata "-Ueeprom:w:C:\Users\nptdns\AppData\Local\arduino\sketches\D94BAE26C110680506C024430865388A/Program_ingrijitor_de_floare.ino.eep:i" "-Uflash:w:C:\Users\nptdns\AppData\Local\arduino\sketches\D94BAE26C110680506C024430865388A/Program_ingrijitor_de_floare.ino.hex:i"
Avrdude version 8.0-arduino.1
Copyright see https://github.com/avrdudes/avrdude/blob/main/AUTHORS
System wide configuration file is C:\Users\nptdns\AppData\Local\Arduino15\packages\MiniCore\tools\avrdude\8.0-arduino.1\etc\avrdude.conf
Using port : COM3
Using programmer : urclock
Setting baud rate : 115200
AVR part : ATmega328P
Programming modes : SPM, ISP, HVPP, debugWIRE
Programmer type : Urclock
Description : Urboot bootloaders using urprotocol
Protocol : STK500v1 skeleton
AVR device initialized and ready to accept instructions
Error: protocol expects OK byte 0x10 but got 0x00 in ur_readEF()
Error: bootloader might be optiboot 4.4? Please use -x bootsize=<num>
Error: unable to read signature data for part ATmega328P (rc = -1)
Error: unable to read signature data (rc = -1)
use -F to override this check
Error: protocol expects sync byte 0x14 but got 0x00
Avrdude done. Thank you.
Failed uploading: uploading error: exit status 1