Using the template for Rmd, I add toc: true to the yaml, and the document knits, but there is no toc to be found. Instead the text “true” appears in the document.

---
title: "Untitled"
author: "Author Name"
date: "2024-08-06"
output: html_document
toc: true
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

## R Markdown

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.

When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

```{r cars}
summary(cars)
```

## Including Plots

You can also embed plots, for example:

```{r pressure, echo=FALSE}
plot(pressure)
```

Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.

A slightly altered yaml doesn’t help:

---
title: "Untitled"
author: "Author Name"
date: "2024-08-06"
output: 
  html_document:
  toc: true
---

The text “true” disappears, but there is no TOC. Ideas?

> sessionInfo()
R version 4.4.0 (2024-04-24 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 10 x64 (build 19045)

Matrix products: default


locale:
[1] LC_COLLATE=English_United States.utf8  LC_CTYPE=C                             LC_MONETARY=English_United States.utf8 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.utf8    

time zone: America/Los_Angeles
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] jsonlite_1.8.8     dplyr_1.1.4        compiler_4.4.0     promises_1.3.0     tidyselect_1.2.1   Rcpp_1.0.12        stringr_1.5.1      later_1.3.2        jquerylib_0.1.4   
[10] yaml_2.3.8         fastmap_1.2.0      mime_0.12          R6_2.5.1           plyr_1.8.9         shinyjs_2.1.0      generics_0.1.3     knitr_1.47         tibble_3.2.1      
[19] shiny_1.8.1.1      bslib_0.7.0        pillar_1.9.0       rlang_1.1.3        utf8_1.2.4         cachem_1.1.0       stringi_1.8.4      xfun_0.44          httpuv_1.6.15     
[28] sass_0.4.9         cli_3.6.2          magrittr_2.0.3     shinyWidgets_0.8.6 digest_0.6.35      rstudioapi_0.16.0  xtable_1.8-4       lifecycle_1.0.4    vctrs_0.6.5       
[37] evaluate_0.23      glue_1.7.0         rsconnect_1.3.1    fansi_1.0.6        reshape2_1.4.4     rmarkdown_2.27     tools_4.4.0        pkgconfig_2.0.3    htmltools_0.5.8.1