Tables in an output don't have borders

[franceskoi]

When I make tables (both row markdown and inserted from Excel via code chunk) in Source, and Knit an .Rmd document, the output document (Word, PDF, HTML) has only text that tables contain, but table borders are not shown.
I use the code from some examples on the web that work since I see the results in the examples, and their tables have borders, but mine don't.
I use TinyTex and have Windows.
I also tried the code on my friend's computer who also has Windows, and the tables are also output without borders. Does that have something to do with the OS we are using? Can you help me solve this problem?

Checklist

When filing a bug report, please check the boxes below to confirm that you have provided us with the information we need. Have you:

• formatted your issue so it is easier for us to read?

• included a minimal, self-contained, and reproducible example?

• pasted the output from xfun::session_info('rmarkdown') in your issue?

• upgraded all your packages to their latest versions (including your versions of R, the RStudio IDE, and relevant R packages)?

• installed and tested your bug with the development version of the rmarkdown package using remotes::install_github("rstudio/rmarkdown") ?

[yihui]

Your issue may be the same as #2567. Could you read and follow the issue guide exactly to provide all the required information? As requested, please do not ignore or delete the issue guide in your post, otherwise it is usually hard for us to help you. Thanks!

[github-actions]

This old thread has been automatically locked. If you think you have found something related to this, please open a new issue by following the issue guide (https://yihui.org/issue/), and link to this old issue if necessary.