Posted by Tobi on Feb 10, 2021; 4:14pm
URL: https://discuss.asciidoctor.org/Unable-to-install-asciidoctor-pdf-tp8487p8489.html

I understand now that this is a compatibility issue. I'll try the pre-release and see what happens. I can still use Ruby 2.x if I get in trouble.
Thank you for your quick help!