You can use lubridate.
By the way, post code, not screenshots of your code or data. It makes it easier for people to answer your question.
library(tidyverse)
library(lubridate)
df <- tibble(started_at = c(ymd_hm("202007091522", "202007242356")),
ended_at = c(ymd_hm("202007091525", "202007250020"))
)
df %>%
mutate(minutes_between = interval(started_at, ended_at) / minutes(1))
# A tibble: 2 x 3
started_at ended_at minutes_between
<dttm> <dttm> <dbl>
1 2020-07-09 15:22:00 2020-07-09 15:25:00 3
2 2020-07-24 23:56:00 2020-07-25 00:20:00 24