mean across all columns

tidyverse
2

Here is an example of how to do it using the built-in iris data set

library(dplyr)

iris %>% 
    summarise(across(.cols = where(is.numeric),
                     .fns = mean,
                     rm.na = TRUE,
                     .names = "{.col}_mean"))
#>   Sepal.Length_mean Sepal.Width_mean Petal.Length_mean Petal.Width_mean
#> 1          5.843333         3.057333             3.758         1.199333

Created on 2022-03-16 by the reprex package (v2.0.1)

If you need more specific help, please provide a proper REPRoducible EXample (reprex) illustrating your issue.