There seems to be a colon and a space missing from the citation.

I think it should be:

Terry Therneau, Steven Hart and Jean-Pierre Kocher (2022). Calculating samples: Size estimates for RNA Seq studies. R package version 1.36.0.

See below for the current output:

citation("RNASeqPower")

To cite package 'RNASeqPower' in publications use:

  Terry Therneau, Steven Hart and Jean-Pierre Kocher (2022).
  Calculating samplesSize estimates for RNA Seq studies. R
  package version 1.36.0.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {Calculating samplesSize estimates for RNA Seq studies},
    author = {Terry Therneau and Steven Hart and Jean-Pierre Kocher},
    year = {2022},
    note = {R package version 1.36.0},
  }

sessionInfo( )

R version 4.2.0 (2022-04-22)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Pop!_OS 22.04 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.10.0
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.10.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] 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   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods  
[7] base     

loaded via a namespace (and not attached):
[1] compiler_4.2.0 tools_4.2.0