Hi, my name is Qian, and I am experiencing a similar problem here.
I can see that my RNA.pm is in this directory: /share/apps/ViennaRNA-2.1.7/compile-install/lib/site_perl/5.14.2/x86_64-linux-thread-multi/RNA.pm

I have posted a more detailed question on the StackOverflow if that helps: https://stackoverflow.com/questions/62050749/viennarna-packages-perl-module-rna-pm-is-required

Can you please elaborate more on "use a 'use lib' statement or set the PERL5LIB environment variable to tell perl where that library is. Or you need to install the RNA library." I don't fully understand how I should do that. Thanks in advance for any help and sorry if this is a very basic question!