To cite flexlsx in publications use:

  Heidler T (2023). “flexlsx: Adding flextables to Excel.” Heidler,
  Tobias (2023). flexlsx: Adding flextables to Excel,
  https://github.com/pteridin/flexlsx,
  <https://github.com/pteridin/flexlsx>.

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {flexlsx: Adding flextables to Excel},
    author = {Tobias Heidler},
    year = {2023},
    url = {https://github.com/pteridin/flexlsx},
    note = {Heidler, Tobias (2023). flexlsx: Adding flextables to Excel, https://github.com/pteridin/flexlsx},
  }