Subtract a column of dates with other columns in R

This is a table that I have where I would like to subtract the dates from the column "Sub" with the columns D1, D2 and D3. the dates have been converted into Date from character using as.Date. I would like the result to be the days between the dates.

Could you please help me out.

library(tidyverse)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union

df <- read_table("PID   Sub D1  D2  D3
123 2015-02-26  2018-04-26  2015-02-26  2014-05-29
345 2014-03-11  2019-05-18  NA  2012-08-11
678 2016-01-22  2017-11-20  2016-01-21  NA
987 2020-06-15  NA  2018-08-19  2019-01-15")

df %>% 
  mutate(across(D1:D3, ~ .x - Sub))

#> # A tibble: 4 × 5
#>     PID Sub        D1        D2        D3       
#>   <dbl> <date>     <drtn>    <drtn>    <drtn>   
#> 1   123 2015-02-26 1155 days    0 days -273 days
#> 2   345 2014-03-11 1894 days   NA days -577 days
#> 3   678 2016-01-22  668 days   -1 days   NA days
#> 4   987 2020-06-15   NA days -666 days -517 days

^{Created on 2022-06-29 by the reprex package (v2.0.1)}