I finally figured it out, it's apparently a bug in the Jerboa for Lemmy app when I try tapping the link posted in Jerboa. Jerboa sees PDF, Jerboa blindly tries to open it as PDF. When I copy the link and paste it into Fennec directly, the link and age verification script works as expected.

So the only thing I was doing 'wrong' was by tapping the link in Jerboa, like why would I expect the simple act of tapping a link is somehow messed up in Jerboa..?

Anyways, thanks for all the 'help', accusing me of being a liar and all. I sure hope you and others accusing me of lying never get into tech support, nothing will ever get fixed or solved that way.