Content hidden not working as expected in index.qmd

[fredguth]

Maybe I understood something wrong, but I imagined that if I used :

::: {.content-hidden unless-format="html"}

<!-- Q:  Why is this appearing on PDF? -->
# Welcome {.unnumbered .unlisted}

 This is the website companion for [my dissertation](./IBToDL.pdf).

 It is yet not finished, but I decided to publish it online anyway.

 This version is being built with [Tufte-Quarto](http://github.com/fredguth/tufte-quarto). 

[![The emergence of an Information Bottleneck Theory of Deep Learning](cover.svg){.column-margin #fig-cover}](./IBToDL.pdf)


:::

in index.qmd, the content should not appear in pdf, but it does.

In any other qmd file it work as expected.

I created a minimum working example repo to illustrate: https://github.com/fredguth/quarto-mwe
This is the same problem reported here: #3047

The motivation to add a hidden section in the index.qmd is to have a companion website to a book project that welcomes in html, but not in pdf (see: https://fredguth.github.io/IBToDL/).