I have also problems compiling your document.
Working with tinytex as you do some packages are installed but at last the compile fails with
! Package fontspec Error: The font "SimHei" cannot be found.
! kpathsea:make_tex: Invalid filename `KaiTi/OT:script=hani;language=dflt;', contains ':'
! kpathsea:make_tex: Invalid filename `KaiTi/B/OT:script=hani;language=dflt;', contains ':'
! kpathsea:make_tex: Invalid filename `SimHei/OT:script=hani;language=dflt;', contains ':'
! kpathsea:make_tex: Invalid filename `SimHei/I/OT:script=hani;language=dflt;', contains ':'
! kpathsea:make_tex: Invalid filename `SimHei/OT:script=hani;language=dflt;', contains ':'
Error: LaTeX failed to compile charliechen.tex. See https://yihui.org/tinytex/r/#debugging for debugging tips. See charliechen.log for more info.
Execution halted
However skipping xelatex for the default engine pdflatex works for me:
output:
pdf_document: default
I do not know if you had a particular reason for chosing xelatex?
Update :
> sessionInfo()
R version 4.0.2 (2020-06-22)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18363)