To cite package lidR in publications use both:

  Roussel, J.R., Auty, D., Coops, N. C., Tompalski, P., Goodbody, T. R.
  H., Sánchez Meador, A., Bourdon, J.F., De Boissieu, F., Achim, A.
  (2020). lidR : An R package for analysis of Airborne Laser Scanning
  (ALS) data. Remote Sensing of Environment, 251 (August), 112061.
  <doi:10.1016/j.rse.2020.112061>.

A BibTeX entry for LaTeX users is

  @Article{,
    author = {Jean-Romain Roussel and David Auty and Nicholas C. Coops and Piotr Tompalski and Tristan R.H. Goodbody and Andrew Sánchez Meador and Jean-François Bourdon and Florian {de Boissieu} and Alexis Achim},
    title = {lidR: An R package for analysis of Airborne Laser Scanning (ALS) data},
    journal = {Remote Sensing of Environment},
    volume = {251},
    pages = {112061},
    year = {2020},
    issn = {0034-4257},
    doi = {10.1016/j.rse.2020.112061},
    url = {https://www.sciencedirect.com/science/article/pii/S0034425720304314},
  }

  Jean-Romain Roussel and David Auty (2024). Airborne LiDAR Data
  Manipulation and Visualization for Forestry Applications. R package
  version 4.1.3. https://cran.r-project.org/package=lidR

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {Airborne LiDAR Data Manipulation and Visualization for Forestry
Applications},
    author = {Jean-Romain Roussel and David Auty},
    year = {2024},
    note = {R package version 4.1.3},
    url = {https://cran.r-project.org/package=lidR},
  }