I get the same error with the Itch build: it's due to the fact that on Linux file extension is secondary/cosmetic (contrary to Windows) and files need to be marked as executable to run. The Steam build launches fine on the same machine because every file is marked executable (not ideal but hey). Now, the easy way for you would be to use plus-x by Cheeseness and mark the following files inside the zip archive as executable:
- linux64/chrome_crashpad_handler
- linux64/nacl_helper
- linux64/nacl_helper_bootstrap
- linux64/somnaBuster
Hope that helps.