not working

Hi, i am currently trying to figure out something that does not work.
I have a topic going on this at the WP general help forum
https://ww.wp.xz.cn/support/topic/what-is-actually-going-on-with-in-39
but i want to try this at your side as well, all be it, i have tested to many Themes on this issue to think this would be a flaw of Tempera.

I have found the necessary PHP line
<?php wp_link_pages(); ?>
in your Theme so the next page should work – but it does not and did not in any of the other 20 or so Themes i tested and tried before, that is why i assume this is something concerning the latest WP update, not your Theme – but still i have some small hope i eventually find out, from one source or another, what is the problem and most of all how to get this working again???