c_across() works inside of mutate_rowwise(). It uses tidyselect so
you can easily select multiple variables.
c_across(cols = everything())df <- data.table(x = runif(6), y = runif(6), z = runif(6))
df %>%
mutate_rowwise(row_mean = mean(c_across(x:z)))
#> # A tidytable: 6 × 4
#> x y z row_mean
#> <dbl> <dbl> <dbl> <dbl>
#> 1 0.402 0.290 0.0514 0.248
#> 2 0.196 0.678 0.530 0.468
#> 3 0.404 0.735 0.696 0.612
#> 4 0.0637 0.196 0.689 0.316
#> 5 0.389 0.981 0.0312 0.467
#> 6 0.976 0.742 0.226 0.648