If you run a (recent) Linux, and you type `pngcheck` (with no arguments) what version number do you get? Feel free to respond with your Linux distro, if you want.
4.0.1
4.0.0
3.0.3
earlier than 3.0.3
Poll ends at .

@svgeesus On Fedora 43, not installed by default, available via package repositories:

pngcheck.x86_64 4.0.1-1.fc43 updates