using libpd

The only libpd I can find is the Pure Data embedable audio synthesis library. But that is BSD, not GPL. See: github.com/libpd/libpd/blob/master/LICENSE.txt

I would like to know if an iOS App using libpd has a chance to pass the notarization.

What’s your specific concern?

It's a GPL Library.

The notary service does not check licencing requirements.

Coding only in Objective C or Swift would be a horror.

Nor does it care about what language you write your code in [1].

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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

[1] It does require the hardened runtime, which enables security features that often conflict with dynamic language runtimes, but you can use hardened runtime exception entitlements to opt out of those security features.