As pointed out before, “your Application” must be GPL licensed and “your Application” refers to the binary application.
12.1. Application(s): desktop or mobile applications developed using the JUCE Code,
which incorporates the Licensee Content.
But the code itself can be licensed with a GPL compatible license. Modified parts or derivative works of the JUCE code base must strictly be GPL:
1.8. Remember, unless you upgrade to JUCE Indie or JUCE Pro, if you exceed the
Revenue Limit for JUCE Personal, then your JUCE Personal licence is governed by the
GNU License which is an open-source licence and requires, among other things, that
you make your source code available and license modified files and larger derived works
(including all linked code) under the same terms of the GNU License. Please review the
terms of the GNU License carefully.