Same issue here. sessionInfo() output:
R version 4.0.2 (2020-06-22)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Arch Linux
Matrix products: default
BLAS: /usr/lib/libblas.so.3.9.0
LAPACK: /usr/lib/liblapack.so.3.9.0
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] compiler_4.0.2 htmltools_0.5.0 tools_4.0.2 yaml_2.2.1 rmarkdown_2.3 knitr_1.29 xfun_0.16
[8] digest_0.6.25 rlang_0.4.7 evaluate_0.14
Other user post a solution here, but not work for me.
[EDIT]: I found a solution that works for me.
In the folder ~/.config/RStudio there's a file called desktop.ini. Change the value of font.fixedWidth key and restart RStudio. In my case, font.fixedWidth=Fira Code.