use print.data.frame(df)
as suggested in Why do tibbles and data.frames display decimal places a bit differently? - #2 by danr
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
df <- tibble(
x_as_character = c("0.1232456789", "0.9101112131415")
) %>%
mutate(x_as_numeric = as.numeric(x_as_character))
options(digits=15)
print.data.frame(df)
#> x_as_character x_as_numeric
#> 1 0.1232456789 0.1232456789000
#> 2 0.9101112131415 0.9101112131415
Created on 2022-02-27 by the reprex package (v2.0.1)