gnutls uses libidn2 internal symbols which were dropped
gnutls when compiled with an older to 2.0 libidn2 will use
_idn2_punycode_decode which is not an exported symbol of the library and has been dropped in the later versions.
Relates to libidn/libidn2#74 (closed)
I'm proposing to no longer use this symbol in gnutls, and drop compatibility with older libidn2 versions.