This is a CSS issue, observed on Firefox 84 and Chromium 87, occuring when a <syntaxhighlight> tag is used and when there are some <div style="float:right"> containing links and these links are horizontally aligned with the <syntaxhighlight> tag: the link is not clickable.

My description is perhaps a bit abstract, so take https://www.mediawiki.org/wiki/Extension:ParserFunctions and try to click on links in the infobox horizontally aligned with the PHP code snippets: you should not able to click (or this issue depends on the browser). With the screenshot below, I cannot click on “License” but I am able to click on “Download extension”.

There is no issue when the <syntaxhighlight> tag is replaced by wikitext-native syntax for code (with a space as first character), see the screenshot below (created with Special:ExpandTemplates with the wikitext “{{Extension:ParserFunctions}}” and replacing the <syntaxhighlight> tag by an initial space) (NB: the screenshot shows a normal cursor but it was really a “hand” cursor with the tooltip below)