Quarto does not render flextable greek letters to pdf

[emstruong]

---
title: "Test"
format: pdf
pdf-engine: xelatex
---

```{r}
library(flextable)
```
```{r}
# set_flextable_defaults(fonts_ignore=TRUE)
data.frame(b = rnorm(2,2)) |>
  flextable() |> 
  add_header_row(values = "\U1D6FD")

```

Here is my sessionInfo() output

R version 4.2.1 (2022-06-23)Platform: x86_64-pc-linux-gnu (64-bit)Running under: Ubuntu 22.04.1 LTSMatrix products: defaultBLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.10.0LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.10.0locale:[1] LC_CTYPE=en_CA.UTF-8LC_NUMERIC=C[3] LC_TIME=en_CA.UTF-8LC_COLLATE=en_CA.UTF-8[5] LC_MONETARY=en_CA.UTF-8    LC_MESSAGES=en_CA.UTF-8[7] LC_PAPER=en_CA.UTF-8LC_NAME=C[9] LC_ADDRESS=CLC_TELEPHONE=C[11] LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=Cattached base packages:[1] stats     graphics  grDevices utils     datasets  methods   baseother attached packages:[1] flextable_0.7.3loaded via a namespace (and not attached):[1] Rcpp_1.0.9digest_0.6.29     R6_2.5.1jsonlite_1.8.0[5] magrittr_2.0.3    evaluate_0.16     zip_2.2.0gdtools_0.2.4[9] rlang_1.0.4stringi_1.7.8     cli_3.3.0uuid_1.1-0[13] data.table_1.14.2 rstudioapi_0.14   xml2_1.3.3rmarkdown_2.16[17] tools_4.2.1stringr_1.4.1     officer_0.4.3     xfun_0.32[21] yaml_2.3.5fastmap_1.1.0     compiler_4.2.1    systemfonts_1.0.4[25] base64enc_0.1-3   htmltools_0.5.3   knitr_1.402

For what it's worth, it seems like Quarto should be using xelatex as the default: