In general a properly accessible HTML should also create an accessible PDF file. There are some potential problems listed down below.
Do not forget to check your created files using a validator like VeraPDF, PDF4WCAG or PAC (Windows only)
The created files should be PDF/A-2a compliant. They should also comply with PDF/UA-1 (except for the metadata indicating this compliance). Compliance with PDF/UA-2 is not possible as we create PDF 1.7 files and PDF/UA-2 requires PDF-2.0. PDF-2.0 is not compatible with PDF/A-2a.
Weasyprint does not support creating <a>-tags that surround multiple elements in a PDF/UA compliant way.
This is actively being worked on by weasyprint.
Sometimes it also works to replicate the <a>-tag in every nesting layer. E.g. instead of
<a><h2><span>bla</span></h2></a> use <a><h2><a><span><a>bla</a></span></a></h2></a>
I'm very unsure of how the footnotes should work in an accessible pdf, but I'm mostly sure the current implementation is not that accessible (the footnotes are in the flow where they are in the page not where they are references. Not yet sure how to fix this.