To cite gtsummary in publications use:

  Sjoberg DD, Whiting K, Curry M, Lavery JA, Larmarange J. Reproducible
  summary tables with the gtsummary package. The R Journal
  2021;13:570–80. https://doi.org/10.32614/RJ-2021-053.

A BibTeX entry for LaTeX users is

  @Article{gtsummary,
    author = {Daniel D. Sjoberg and Karissa Whiting and Michael Curry and Jessica A. Lavery and Joseph Larmarange},
    title = {Reproducible Summary Tables with the gtsummary Package},
    journal = {{The R Journal}},
    year = {2021},
    url = {https://doi.org/10.32614/RJ-2021-053},
    doi = {10.32614/RJ-2021-053},
    volume = {13},
    issue = {1},
    pages = {570-580},
  }