The links generated for the table of contents in PDF are not are accessible for screen readers such as Orca of NVDA in an exported PDF. This may be a bug.
Source file used to export to PDF with Universal access option selected: TOC-not-clickable-for-screenreader.odt
I have tested with the screen reader Orca.
Any help will be greatly appreciated.
Which help do you expect here on this user-to-user site related to the very specific and interesting problem you are reporting? this is a bug (or rather enhancement request), which should be reported appropriately.
I see you have filed tdf#142376. Great! Could you also provide a sample PDF (if you have such) with links that are readable by the screen readers? Attaching it there in the bug for comparison could be immensely helpful for whoever decides to fix it.