### Bug description

When using `pptx` as an output format, `mermaid` isn't rendering. 

A minimal `.qmd` file with an example is below:

````
---
title: "Mermaid not rendering"
format: pptx
---

## Mermaid won't render

```{mermaid}
graph LR
A[Hello] --> B[World]
```
````
The resulting PowerPoint contains the title of the slide, but not the diagram:
[mermaid-pptx.zip](https://github.com/quarto-dev/quarto-cli/files/8914092/mermaid-pptx.zip)

I'm running `Ubuntu 20.04.4 LTS` on WSL2.  
Output from `quarto check`:
```
[✓] Checking Quarto installation......OK
      Version: 0.9.587
      Path: /opt/quarto/bin

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.8.10
      Path: /usr/bin/python3
      Jupyter: 4.10.0
      Kernels: python3

[✓] Checking Jupyter engine render....OK

[✓] Checking R installation...........OK
      Version: 4.2.0
      Path: /usr/lib/R
      LibPaths:
        - /usr/local/lib/R/site-library
        - /usr/lib/R/site-library
        - /usr/lib/R/library
      rmarkdown: 2.14

[✓] Checking Knitr engine render......OK
```


### Checklist

- [X] [formatted your issue](https://yihui.org/issue/#please-format-your-issue-correctly) so it is easier for us to read?
- [X] included a minimal, self-contained, and reproducible example?
- [X] documented the quarto version you're running, by providing the output produced by `quarto check` in a terminal in your issue?
- [X] documented the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
- [X] documented which operating system you're running? If on Linux, please provide the specific distribution as well.
- [X] upgraded to the latest version, including your versions of R, the RStudio IDE, and relevant R packages?
cscheid
2022-06-15T23:21:15Z
lucas-a-meyer
bug
1.0
closed
Mermaid diagram doesn't render on PowerPoint
https://github.com/quarto-dev/quarto-cli/issues/1159