Yet another stk500_recv() error

I've got an second-hand Elego ATMEGA328-PU (Arduino UNO), Tried to run some stuff on it, but I got this on macOS, |500x403 and on Windows: |375x500

Things like drivers and ports are ok (as far as DeviceManager on Windows says), so the board it is recognized by the laptop(s).

Other people on internet with the same problem say I should go to Tools -> Processors and switch to the "old" bootloader.

I do not have Tools -> Processor tab either on Windows or macOS, What should I do ?

https://arduino.stackexchange.com/questions/17/avrdude-stk500-getsync-not-in-sync-resp-0x00-aka-some-dude-named-avr-won

tried the accepted answer from here, and it didn't work.

serghey: Other people on internet with the same problem say I should go to Tools -> Processors and switch to the "old" bootloader.

I do not have Tools -> Processor tab either on Windows or macOS,

That advice only applies to the Arduino Nano. Since you have the Uno it is normal and expected that there is no Tools -> Processor option.

serghey: https://arduino.stackexchange.com/questions/17/avrdude-stk500-getsync-not-in-sync-resp-0x00-aka-some-dude-named-avr-won

tried the accepted answer from here, and it didn't work.

Did you even try the "burn the bootloader" part of that answer?

Did not have a device to do that at the time, It eventually worked after re-programming it following this tutorial: https://wspublishing.net/avr-c/restoring-arduino-uno-bootloader/ Thank you,