AWS IoT Device Tester for AWS IoT Greengrass V2 Test failed with error: failed to validate lambda publish: timed out

If you set up folder permission as recommended in above comment sudo chmod 755 folder-name, you can also try with --timeout-multiplier command, which also can be found in the troubleshooting page.

I've seen this error reported before for older GG nucleus versions. Besides the error you reported, I think you may also have a Error: Could not find or load main class in your idt-ggv2-lambda-function-idt.log file. If so, I think the root cause may be folder permissions.

https://docs.aws.amazon.com/greengrass/v2/developerguide/idt-troubleshooting.html#test-timeout

If the MQTT or Lambda component logs contain Access denied errors, your Greengrass installation folder might not have the correct file permissions. Run the following command for each folder in the installation path that you defined in your userdata.json file. sudo chmod 755 folder-name